I've not soldered a computer cable since the 1980s
and I was rubbish
at it then. And even so, I have no source for the relevant connectors!
For the last part, RS components, Farnell, Digikey???
For the first part, I'd offer to do it for you, but it would be illegal
to do so. Owing to our totally daft laws, (a) I'd have to use lead-free
solder, which I don't have, don't trust, and am not set up to use and (b)
it has been said that if an enthusiast (specifically a model engineer,
but it would apply here too) does jobs for others, then his workshop
becomes a workplace and is covered by all the daft health-and-safety
rules that I have no desire to get involved with, and which quite
honestly, would stop me from getting on with things.
-tony