Bacta export is dominated by Omega Pharmaceuticals and, to a lesser extent, Silk Holdings; the latter also dominates the kolto export market. There are possible alternatives -- other corporations and other substances that might make a play for galactic market share -- and it would be interesting to see them try. In the meantime, so far as I know it, this is the state of the galactic bacta and kolto markets, as well as some notes on other substances.

BACTA​

Since the (debatable) end of the Dark Age, bacta production in the galaxy has been dominated by Omega Pyre/Omega StarCorp/Omega Pharmaceuticals’ Thyferra holdings. OSC claims to own most of Thyferra in the same way they claim to own Fondor and a few other crucial worlds in former OP space. Though I have my share of history with OP -- I served with the ODF for years -- I felt sort of compelled to shake up that monopoly.
Enter the galaxy’s other major player in bacta: Silk Holdings, the company I built with my wife, the company we walked away from. There’s a lot of history there involving Tionese investment and a lot of space tape, but in the end, Silk bacta from the forgotten planet Verkuyl became a viable competitor in some markets.
Iron Crown Enterprises, though not a bacta producer, latched onto Verkuyl in recent years; it produces a ton of bacta tanks, purification equipment, and other bacta-related goods, and its distribution networks are second only to Arceneau (and better in the Unknown Regions). Several other companies have dabbled in bacta peripherals and distribution, including Merr-Sonn, Skel Medical, and even a mildly resurgent Zaltin Corporation.
To sum up: most of the bacta you use is from OSC/Thyferra. A good portion of it is from Silk/Verkuyl, especially if you’re in or near the Unknown Regions. So far, no serious challenger has emerged, though I’d be interested to see someone try.

KOLTO​

Kolto is somewhat less effective than bacta. By careful manipulation of production and price points, though, the Selkath have managed to make it a competitive export. When you’re out on the fringes and you can fill two or three kolto tanks for the price of one bacta tank, the Selkath stuff looks appealing. That’s the foundation of the partnership my wife and I developed with the Selkath years and years ago, when we were still building the Mara Corridor and Silk Holdings.
As a side note, a Huttese company called Semper Medtech, out of Kessel, dabbles in kolto accessories and derivatives. By and large, however, Silk remains effectively unchallenged in the galactic kolto market. It doesn’t hurt that Silk has a longstanding monopoly on kolcta, the expensive kolto/bacta derivative that leaves even apex non-export bacta in the shade.
Other worlds around the galaxy, such as Ceto and Iferetes, produce kolto in small amounts. This is possible through a longstanding partnership of Selkath colonies and ancient Firaxan sharks. Silk, by hook or by crook, captured one-hundred-percent export market share among these worlds after I left.
Manaan has been invaded a few times, and Ahto City has been devastated twice. Both times, the Silk/Selkath bacta facility in Ahto City was deliberately targeted by Republic defenders and their allies. During the final One Sith assault, the Progenitor was captured and killed. Shockwaves traveled through the entire kolto industry; bacta increased its relative market share. Through unknown means, Silk and the Selkath made an agreement with two ancient Firaxa sharks from other Selkath colonies to return to Manaan and take the Progenitor’s place. Kolto production continues, but the kolto industry may never be the same.

OTHER SUBSTANCES OF NOTE​

I’ve heard of modern substances that surpass kolcta, but from what I can tell they’re all vanishingly rare and have a host of side effects. I think one’s called aspha serum. I haven’t tried it personally, but I hear it saves lives. I believe it’s bound up in that Arceneau-backed medical charity that’s making waves lately.
I’m told a company named Illustrio brews something called gamarita, slightly cheaper and slightly more effective than export bacta, but with side effects attached.
The Kiribi corporation Panacea was cut off from bacta and kolto supplies during the Dark Age, and developed some comparable proprietary treatments.
Pydyrian healing sticks, though not as effective as bacta or kolto, are still a solid resource with a niche market in a chunk of SSC territory. Maybe one day they’ll go big. There are certainly uses for a solid-state equivalent to bacta and kolto.