Found some on eBay. 5 bux. That's cheap enough to be under my DIY threshold.
I ordered 2, but I forgot to check the length, so I might have to DIY some longer ones.
I checked with elektron and the a4 only sends start and pulse. Makes sense because the DIN that sends other signals must(?) use the other pins and this way MIDI and DIN don't use the same pins.
I ordered 2 because then I can do stuff like run the out port at 24 and thru at 48. And probably not, but maybe elektron will add 12, 8, 4, 16 later.
DIN start just being +5v won't be hugely interesting, but I have enough utility modules (thanks Doepfer!) that I should be able to do some neat stuff with it, like invert, attenuate, delay, mix, gate, etc. Plus, the a4 works stopped so I could even work stopping the a4 into performance. Either way, it's great to have options.
If anyone does want to DIY I found this while researching:
http://www.rv0.be/sudc.html