Typically, a DC powered router has power brought to it, it doesn't "plug in" or need a cable for it. The typical wire used to bring power to it is stock THHN sold everywhere, you can buy it by the foot at Home Depot/Lowes. Just get something like 14AWG or 12AWG THHN. Stranded is alot easier to work with rather than solid.
You just route the wires down from your DC fuse panel at the top of your rack fed from your DC plant..
But, my guess is that you need DC power at -48V in the first place? There's going to be plenty of rectifiers available on eBay, DC power isn't that unusual for many activities outside of networking.. This one looks fairly cheap and sources enough juice.. (be careful of the terminals, it looks like the AC ones are bare? probably meant to be stuffed into a NEMA box of somekind)
The 2611-DC seems to take 2A per the data sheet. Just connect the + output to the common input on the router, and the - output to the -48V input on the router).
Or something like
is from a telco vendor which is the large consumer of -48V DC power.. Probably for a small item that would be out in the field away from the DC plant in the first place.. But it also just covers the input needs of the router. Probably be fine, I'm sure the router doesn't draw its max current anyway. I'd probably go for the Tellabs one myself.
Get a couple foot length chunks of THHN (red and black) and connect it up with the right polarity (checking with your VOM) to have -48V go to the input side of the router.
Does anyone know if it is possible to swap out the DC power supply for an AC power supply? I don't think the AC power supplies are expensive (they'd probably cost me the same as buying all the paraphernelia for running DC power)