Greg,
Thanks - you're an expert/professional/do this for a living, I'm just a potterer.
The 10k pot was recommended in the i-Mic design (the link is somewhere above) and as I am just 'fiddling', I use elements from old phones - because they work and they're free.

They behave like the LoZ mics I have (SM58) so I assume they're LoZ.
Jaycar (not sure if they're just Aussie or are in the US as well) sell all sorts of hobbyist electrical components and I'm always buying 1/4" jacks or switches and pots for mics or speaker cabs or whatever I'm fiddling with at the time. They've got 9mm pots in 1K, 10K, 50K and 100K - log or linear, single or double gang. Cost $3.25 (inc tax) so they don't break the bank! And they're only 10 mins from work.
Thanks for the input. That's the joy of this sort of site - the real experts help us 'mug amateurs' with advice