Simon is the owner of Convoy Flashlights. He is also present in this forum and often does special builds for customers on request. The way maybe to do it is ordering an S12 on his aliexpress website, but not pay it but instead write a message to him in the order page asking for the different leds. If you are lucky he will be willing to build you the UV S12 (he does not have a UV-pass filter in the S12 size so that you will have to do yourself) and will adjust the price accordingly. Then you pay.
https://convoy.nl.aliexpress.com/store/330416
But maybe you can ask Simon directly in the Convoy thread on BLF: 【convoy】S21E XHP50.3 HI available now