The RAMC, RADC & QARANC have had new TRF's based on thier stable belt colours approved by the Army Dress Committe in August 2006.
Most Formation Signs, DZ Flashes and TRF's are not supplied items and do not therefore have NSN's. They are a Regimental Item and sourced by the unit with public or regimental funds. Your Adjutant or QM (not his storeman) should know the procedure.
As yo say, a nominal role of attached personnel, sent to thier Corps HQ will get you an allocation. Same for your own corps I should think!
It works if you know you're in the right and have a bit of spine. I was at JHSU in the mid-90s and our SSM tried to instigate some sort of unit patch before all this TRF nonsense erupted (the only people who had them then were mainly 5 AB Bde and the Household Div) and we would have had to have paid for all of them, there was no free first issue. One of the young Lance Bombardiers basically said if you want me to wear it, issue it. The Stick Man went a bit radio rental, but our Ord Rm Clerk had a set and told the him that it was unenforceable. Cue much blood pressure but no paying for patches.