In my restoring and collecting of Simpson 260s, I often face the same challenge.   

Sometimes I get lucky and find new Simpson test lead sets for sale with the right connectors.  I try not to pay more than $20 for a pair of new ones, but that requires diligent searching. 

Other times I have to make new test leads from scratch with wire, probes, and connectors.

When I need to make a set, I've learned to look for wire that specifically calls itself "test lead" wire.  I find it has the rubbery, limp character we want in test leads.  Regular hook up wire is frustrating as it coils and twists, and it breaks too soon from the flexing.

The last batch I bought was from Cal-Test Electronics.

Set the length filter to the smaller rolls to see realistic prices for our purposes.

I bought it through Newark, DigiKey, or Mouser I think. 

So far I've used this wire to make some deluxe alligator clip leads (with real Mueller clips) as well as several Fluke and Simpson meter test lead sets.  The wire feels luxuriously limp and is clearly of high quality.