I know the feeling mate, I had given up looking for one of these rails and was looking for something else then stumbled across it.
I hope AG do the updated a3 rail as a kit, I'll definitely get one.
I've been looking for a RS for ages without any luck and stumbled on this today. Thought I'd share.
https://airsoftartisan.com/products/airsoft-artisan-l85-sa80-20mm-picatinny-rail-adapter?_pos=1&_sid=e852f538f&_ss=r
I'm not affiliated with Airsoft Artisan but they do some nice gear.
Jk Army in HK have one, never had any issues when I've ordered from them. Black Friday 10% sale on at the moment.
https://shop.jkarmy.com/vf9-fhr-ops-01.html
I agree mate, it's a pain when something little requires the replacement of a big part. I just thought I'd give you a steer to the replacement.
On the plus side its very realistic, the real steel is constructed with the same 50p sheet metal haha.
KYAIRSOFT do the bare upper part, Part 1. Easy to strip your old and replace with this.
https://www.kyairsoft.com/parts/we-rifles-gbbr/l85-series/l85-1-gbbr.html