It's not sur at 100% that's it's your relay, it can be your fillage too, did you chek with a volt meeter/volt mètre (I don't know the word in english). If you didn't chek test in (parralele) with your voltmetre around your relay and what your fuel pump touch too.
And I think that you can buy a relay in any electronic shop, you'll need the specs of your currents relay and that's it I think.
-Éric