I guess if you're adament some snakes will only eat live then the only other possibility is that snakes that don't take frozen thawed are culled. You'd have to ask a UK breeder if that's the case.
All I know is that in no pet store and on no website will you ever find a snake sold as eating live in the UK.
Nor are live vertebrates sold as feeders.
Again, it might sound strange to you but it's not something that's done here.
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I've still to encounter a snake who won't eat thawed frozen , as long as you feed in the evening and wait until they're nice and settled under the hide , dangle a WARM mouse at the entrance and don't blink.