EAB has a link of Independant Amiga Hardware developers projects, costs, and how to reach them (
http://lilliput.amiga-projects.net/Indie.htm); a few of the links do go back to AmiBay (Yep, heavy handed), but the IDE68K and CFIDE68K (small plug-in adapters that connect to the A500's CPU socket) are good options. AmigaKit has the Clock-port adapter for the same socket, but clock-port devices are hard to find too. I believe there is a A500 expansion port adapter, "Zorro Slot Adapter."
But, my advice: 1) Get her (A500+) open and get that battery out; a coin cell replacement will run 5 bucks. 2) Get 4 MB RAM in (
http://www.kipper2k.com/amigaforsale/index.html), 3) Pick up a Motorola 68010 to play with (do not believe the hype, but it is cheap ($9 on eBay), and 4) Get a KickStart 3.1 ROM (there are eBay copies for about $20 & AmigaKit now has an "Official Copy," or ask a member for one (The cost of the EPROM -- a 27C400 at 105ns runs 6 bucks, 5) Read up on the IDE + CF options. 6) Invest time in becoming a member of this forum, AmiBay.com (you can still avoid being "bitched-slapped"), EAB --
http://eab.abime.net/, and consider looking into sites like "The Zone" -- ftp.Magix.ws, two other sites I won't mention because their legality is of some question, but I would have the same question of EAB's "The Zone". 7) If you read German or can can use Google Translate, then head to the
http://www.a1k.com site for information, hardware projects and such.

Buy the "Amiga Forever 2012 Rev 3" DVD ROM, it will give you legitimate ownership of the ROM's, a registered copy of IDEFix97, WinUAE emulator and a bunch of retro games to try -- only a handful of what is out there.
Remember, Google is your friend and as my college chemistry professor used to say, "Don't just search, Research!"