I was browsing around Alltronics (http://www.alltronics.com/), an online electronics surplus store, and found the following items that may be of interest to Commodore fans:
An Atari numeric keypad. Your C128 doesn't need this, of course, but your C64 might. Especially for only $4.95 + shipping.
http://www.alltronics.com/cgi-bin/item/CX85/118/ATARI%2D10%2DKey%2DNumeric%2DKeypad
An Atari trackball. A bit pricier at $19.95, but these are getting hard to find. CBM compatible, of course.
http://www.alltronics.com/cgi-bin/item/92C069/118/Atari%2DTrackball%2Dfor%2D2600
C-10 (10 minute) cassettes. Perfect for C2N/1530 use, and only a dime apiece!
http://www.alltronics.com/cgi-bin/item/92V024/118/C%2D10%2DCassette%2DTapes
5.25" diskette fileboxes for $1.95 ea. Again, it's getting harder to find these, especially new!
http://www.alltronics.com/cgi-bin/category.cgi?item=DX510E
And they have them for 3.5" diskettes for $1.95
http://www.alltronics.com/cgi-bin/item/DF_1003/search/3%2E5%22%2DDiskette%2DFilebox
TV/game switch for $1.79.
http://www.alltronics.com/cgi-bin/item/04V004/118/TV%2DGame%2DAccessory%2DCable%2DSwitch
6-pin male and female DIN connectors from 50 to 65 cents each, depending on style:
http://www.alltronics.com/cgi-bin/category.cgi?&category=CC&start=10
27xxx series EPROMS for 99 cents and up:
http://www.alltronics.com/cgi-bin/category/27
Dual DB9 (female) to DB9 (male) switchbox. They say it was built for video switching, so now you can hook up TWO C128s to the same monitor! $6.95
http://www.alltronics.com/cgi-bin/item/24C003/67/A%2DB%2DData%2DSwitch%2DDB9%2D2
24 & 28 pin IC test clips (great for CBM ROMs!) $7.95 & $8.95
http://www.alltronics.com/cgi-bin/category.cgi?&category=60&start=10
40-pin clip (CPU, etc.) is $11.95.
http://www.alltronics.com/cgi-bin/item/TC_40/60/40%2DPIN%2DTest%2DClip
Plus they've got your requisite miscellaneous electronics parts, LEDs, LCDs, cables, connectors, surplus PC boards, kits, tools, etc., etc.
DISCLAIMER: I've never ordered from them, but they seem to have a good rep online.
More stuff:
Blaster joystick autofire with adjustable speed, $5.95
http://www.alltronics.com/cgi-bin/item/92C080/14/%22Blaster%22%2DGame%2DAutofire%2DSwitch
DB9M to DB9F monitor/serial cable, $1.39:
http://www.alltronics.com/cgi-bin/item/24W046/14/6%2DWire%2DDB%2D9%2Dmale%2Dto%2Dfemale%2Dcable
Imagic - Injured Engine program for the Commodore 64, $9.95:
http://www.alltronics.com/cgi-bin/item/92C078/14/Imagic%2DInjured%2DEngine
5.25" looseleaf pages for ring binders, $2.99:
http://www.alltronics.com/cgi-bin/item/24V005/14/Ring%2DKing%2DData%2DDefender%2Dloose%2Dleaf%2Dring%2Dbinder