I've made up quite a lot of synthDIY projects over the past few years (though to my shame, I still know next to nothing about electronics), and it's almost always the capacitors that are a pig to get hold of, especially here in the UK.
When self-sourcing, they're always the things I struggle to get hold of from local sources. On this occasion, I just went with DigiKey, as they also had the illuminated switches (an in stock, unlike Mouser).
Here's my DigiKey shared basket:
I actually bought the pots from them, too. Rather than going for the round-shaft Alpha ones from Thonk, I thought I'd try these Panasonic D-Shaft parts, as I'd heard good things about them on Muffwigglers. Haven't soldered them up yet (parts only arrived today), but I have to say, they feel really nice. Lovely and smooth to turn, but not too stiff.
Things you will have to source yourself:
* I'm still not sure if I've got all the required headers. I think I may be missing some
* 14-way IC sockets. They didn't have these, unfortunately, so they're also not in the basket
* Minijack sockets. Thonk probably still best for these
* Knobs. Thonk used to sell lovely Rogan (Mutable Instruments-Style) knobs, but they're sold out, sadly. I can recommend these Cliff parts. They're cheap, but have a nice feel to them (and they're available in a range of colours, too)
I think everything else is there, however (and the majority of the components are identical parts to the ones on the Mouser BOM).