Hi David,
indy pen dance are great and very efficient, i've used them several times. Golden nib i think also does Bock.
As far as i am aware both Bock and Jowo supply all the major manufacturers or have done, but Jowo don't really boast too much or can't, Bock do and list all the big names on their site. The bit i don't understand at all is that they both supply Schimdt nibs and units branded Schmidt but apparently they could be by either but i think the tipping material is a little bit less quality.
I may well be wrong but the feeds from bock, jowo and schimidt seem very similar to me, unless you want ebonite feeds. I may well be wrong though.
I sell a few jowo nibs with feeds, i have been persuaded by Jim to let people know which i will about other things as well shortly, but for now i have #5 and #12 5mm and 6mm respectively nibs and units from Jowo, mainly in gold plated steel in fine, medium and broad i don't have loads of each at all. I can only knock a pound per unit off for forum members only. So they would be £7.50 and £10 respectively delivered. PM me and i will send you a link.
Schmidt would be Ian Jeffrey at Studio pens, but i don't waht stock he has but a very helpful man he is.
Steve i would may be be interested in a bulk buy for kits but it really would depend on which.
Pete