1) nutted brake bolts to convert Shimano recess nut calipers for the older frames.
2) replacement cleats for older, obsolete clipless pedals (specifically for me, MKS Mapstage)
3) premium brake hanger hardware for setting up cantilever brakes.
4) Suntour Superbe Pro 8 speed Accushift replacement cassettes. These are ones that would have the different size spacers for the lower 3 cogs and the the (slightly thicker?) spacer for the larger 5 cogs. Ideally the person who would tackle this task could improve upon the original by making the new one lighter & maybe even quicker shifting. It would also have only a single threaded locking outer cog, not the doubled-up threaded outer cog as seen in the Microdrive series.
5) Uniglide small parts for updating/maintaining older Shimano Uniglide cassettes & freewheels. A batch run of 7403 Dura Ace freehub bodies - the ones that take the proprietary coarse threaded mounting bolt but that are also combo UG/HG compatible would be most welcome
6) classic road triple cranks, modular in style. These could include a quality forged or CNC 5 arm spider to accept modern 130mm Shimano spec chainrings & the normal spec “granny” ring but in a full range of sizes.
7) more reinterpretations on quill or 1” ahead stems that accept 31.8 handlebars.
8) extra pretty brackets for mounting water bottle cages on frames without braze-on bottle bosses.
9) aftermarket Octalink one key release crank bolts.
10) reissues of rare, 1” threaded, sealed cartridge or needle bearing headsets. American Classic, Specialized, come to mind.
11) a new production run of Salsa “Shaft” seatposts in a variety of lengths & diameters.
12) a fresh production run of Mavic Retrofriction shift levers, preferably in anodized colors that mount the Allen head or Torx bolts as opposed to a flat blade screwdriver.
13) bring back the Rhode Gear Flickstand!

This is all I can think of right now.