Reddit mentions of Pebeo Gedeo : Crystal Resin 300ml

Probably worth noting that water clear polyurethanes will be more expensive and more finicky (especially on the mercury-free end), so epoxies may be a reasonable starting point if you don't want to overspend early on.

You could try:

http://www.amazon.co.uk/Easy-Cast-Clear-Casting-Enamel/dp/B003CHQWDW/ref=sr_1_1

...or:

http://www.amazon.co.uk/Pebeo-Gedeo-300ml-Crystal-Resin/dp/B0027J1DB2/ref=pd_cp_diy_2 (people say that this one is a bit slow to cure)

Other than that, you just need some disposable cups and gloves and mixing sticks (tongue depressors, chopsticks, etc) - so you can do fine without buying a kit. Eye protection is prudent, too.

if you have clear resin you could put the spider into a mould with the clear resin like those magazines do that give out bugs in resin I once used this stuff https://www.amazon.co.uk/Pebeo-Gedeo-300ml-Crystal-Resin/dp/B0027J1DB2/ref=sr_1_1?ie=UTF8&qid=1473324884&sr=8-1&keywords=resin

I've seen other UK people's epoxy resin projects using this brand from amazon.co.uk