Too late I know but I emailed Swansea hackspace:
https://swansea.hackspace.org.uk/
Justin Mitchell from there came back earlier but I've only just read it:
"The hackspace does have a small stock of generic bead thermistors, I cannot remember exactly which kind they are but 10k ntc sounds plausible. You are welcome to drop in and check, there is a workshop on today 12-4ish and there is our usual open evening monday 7pm onwards.
Tom whitehouse electrical/spares store in swansea market -might- have something, he has an odd selection of stuff.
many tumble driers and other home goods use ntc thermistors, so you might get one from a spare parts supplier but they may not know what rating it is.
next best urgency is to buy from cpc online as they will next-day you stuff and their minimum order is £5"
Worth knowing for the future. Bet there's a whole new bunch of neeks, nerds, gerds & blerds there that could assist on your madcap ideas! In fact there's one in most towns.