Repair / Replace Gas Lighter and Logs
Certainly parts like thermocouples, gas valves, fans, fan speed regulators, spark ignitors, etc. can be found generically and installed.  In many cases you might need to make a small change to the part, like drilling a new hole for mounting.  In more extreme cases, you might need a specific trades person to manufacture a replacement part for you.

You mentioned that your logs are missing - these are ultimately just ceramic logs and I doubt any specific manufacture is doing something that would make them completely incompatible with another manufacture fireplace.  Whether they will fit or not is really the only question here.

But I would be seriously suspicious of someone who tells you that you need to spend 10k to replace something just because the manufacture is out of business.  This is very common, and unless something is seriously wrong, I very much doubt you need to replace the entire unit.  Even if this were the case, I would strongly recommend you shop around and ensure you are getting a fair price.