hi, we got the 'shock & unlock' from helfrauds, it's their own brand of,.
they go out of stock quite quickly though & i had to phone around the localish stores to find some at one point, it's cheaper than plus gas & we found it to be better, less greasy & worked better/faster,.
getting it undone it was the cheap adjustable spanner that did it in the end!
( after filing an edge on both sides of my nips )
i used a special brake pipe (almost complete ring spanner type thing) 14mm spanner that was great for gripping when i removed the caliper, if they do them in a 7mm that would be very useful to you!
we got the calipers off in the end, bought a rebuild kit £12 or £15 sorry can't remeber exactly, took them apart & rebuilt them, was easier than we thought & has cured & improved our problem, one of our problems anyway
hope that's of some help to you

Around the World in a Tea Daze
1980 1776CT Laurie engine

1992 Leyland Daf panel van camper
1978 Sherpa Autosleeper DeLuxe
Sprite Major Caravan