Tl;dr: the lab I distributed for was the MXE source, thanks to buying precursors at fire sale prices of a closed lab, and we basically monopolized the market. We only did a few production runs and kept selling the stock; when it became illegal in China, I sold everything left to one distributor and I have no idea where it ended up
Hello! I used to be a distributor for a lab in China that primarily synthesized MXE and other analogs. This lab probably accounted for a good portion of the MXE trade during its peak, and we were able to undercut every other lab. I was only aware of 2 other labs that made MXE in very small, custom-order qualities, versus the dozens I can count on my hand for other RCs/analogs. I think we did well during our peak.
I can't give you any details on the lab's history and what it's doing now, but around when MXE started hitting the streets, another lab was having some internal financial issues (internal theft and partners drifting apart, or something). So the remaining partner did a bulk fire sale of everything they had: equipment, precursors, etc. Most of it was snatched up quickly by other labs, especially cyclopentyl bromide (also used to synthesis ketamine), but they had a large supply of 3-methoxybenzonitrile(not really useful for synethizing K, but useful for MXE).
This lab I was affiliated with buys out all the methoxybenzonitrile, and it wasn't too hard obtaining everything else needed through easy legal channels. Synthesizing MXE is actually fairly simple when you have methoxybenzonitrile. We had a few production runs where we ended up with TONS and TONS of MXE, we burned through all of the precursor we brought and ended up with about ~50 L of methoxetamine HCl across all of our production runs; that we turned into powder. Now that is a lot of MXE.
I had pretty stable deals to sell MXE for almost a year, but then it was made illegal in China, and a lot of the distributors I sold to would only buy legal analogs to stay in the clear. I ended up unloading all the remaining MXE I had to one distributor around early 2016, now that should be enough to last for AGES, so either he got arrested and had it seized, or shittons of MXE are still out there in some warehouse.
As for why the lab doesn't make MXE? It was only profitable because we brought the precursor at rock bottom prices; other products make much more money. The demand, from the distributor side, dried up.