building my own relay computer

Punched tape is about. Check out the "green keys" list, 5-level stuff comes up from time to time, generally at low cost. There is some ex-CNC items on E-Bay at present but for silly prices. Whilst I haven't seen any on E-Bay there were three Documation readers advertised on the Vintage Computer forums. slow) Many folks have implemented photo electric tape readers, but these tend to be clocked off the small feed holes. I guess it wouldn't be too hard to build a photo electric reader that has a 3-d printed feed wheel that was driven by a stepper motor. In fact I am pretty sure you could even use a coil and ratchet arrangement, like this one here:- http://grabcad.com/library/cam-operated-ratchet-pawl-1 but operated buy a coil and magnet rather than a rotating cam. Some one has actually made a complete but operated mechanical punch card computer.. http://observationdeck.io9.com/a-3-d-printed-hand-cranked-punch-card-compute r-1481921919 so I don't think its hard. Getting things 3-D printed isn't hard, in fact most FabLabs will have one and things can be printed for the cost of materials. Also Hack Space... I think it's the punch that's harder. You would need to harden the punch pins, and the would need to have a very exact fit. I guess a CNC router could be used to make these...