I've built a couple, i use mouser for the main parts but the digikey list for the 4x jack sockets i got from maplin.co.uk You have file the contacts down a bit as they don't fit through the pcb holes. I found ebay a good source as well for individual bits but the quantities are a bit more. I got 20x thermistors for the ambient probe for about $2 postage included. Still cheaper than maplin or mouser.
Hi, Another part time UK builder here - 50% of my time in Nairobi. I purchased most parts from the US with a few locally from RS and Maplin. I'm awaiting local 3D printing of Tom's Rotary Damper design although I ordered the HM case from him in the US.