Don't quote me on this, since I've been out of the scene for a little while, but I don't think you'll find new caps very easily. Signature plastics DSA profile might work, but I'm not sure if/how they do legending on PBT. I'm almost sure they don't do double-shot PBT. Even then, to order just 200 keys from them would cost you an arm and a leg.
You may or may not be able to use standard cylindrical caps, due to their height and profile. If you could provide us a height measurement of your keycaps, that would be helpful.
If Maltron's stock keys are ABS, I very much doubt they'll be able to produce PBT ones for just one order due to costs.