@Lurch - that's a great tip about modding the A590, I recently started looking on ebay.de and found several of them (the regular North American ebay.com hasn't had a single Amiga 500 hard drive in months).
Any SCSI side car should work, but the trusty old A590 is pretty common :-)
Have bought a few items from Germany, usually quick on postage and theres some really good dealers too. Google translate works well, but most of them speak english so answer your questions fairly quickly.
On the other part, you keep mentioning links on Amibay.
Haven't had any issues with Amibay and the rules are there to protect buyers/sellers. They are a great bunch. The mods are friendly and easy to chat to and have a lot of useful information.
Amibay is a great resource for hardware/contacts. Same goes with EAB. Actually leaning towards EAB/Amibay more these days.
Both sites have information about new hardware that doesn't show up on amiga.org. This never use to be the case but times change I guess. I miss the good ol'days of Amiga.org.
If it wasn't for Amibay I wouldn't have a couple of items I've acquired. Love being able to swap hardware aswell as purchase which isn't possible via Ebay
Although I've made a few contacts through ebay that source amiga gear.
Prices to me seem cheaper on Amibay and a better range of gear to look through.
aminet (docs/hard) has free schematics and guides for most of those 'independent developers projects'.
Problem with docs is it's not actual hardware, I couldn't put one together myself.