As Graham has suggested modelbahnshoplippe (https://www.modellbahnshop-lippe.com) is the best pricing on blank ESU decoders.
You will need a LokProgrammer to program and upload a sound project yourself, or buy a commercially available sound file from the likes of wheeltappersdccsound and burn it yourself onto blank decoders. But for the Fx you probably only need to connect it to your DCC programming/test track so you can adjust CV values and mapping.
modelbahnshoplippe is euro and bypasses any brexitistani delays and costs by avoiding GB retail channels. The sound files for 071 and 201 are free from ESU's own website library as are other US EMD variants that are suitable for 121,141,181 but you'll need your own horn, guards whistle and flange squeal recordings to make up an Irish sounding baby GM. Graham has done a lot of work in this area.