When it comes to wiring kits, I prefer to spec it all out myself as a lot of the kits I've seen include substandard wire, connectors, etc.
What you need is a good quality relay of higher amperage that you can connect using your existing fuel pump relay's activation signal. The old activation signal will become your new relay's field coil activation signal. The power source and feed for the relay should be of a larger gauge wire that allows for higher current capacity. I would probably look at using minimum 10 gauge if not 8 gauge wire since the run to the rear is relatively lengthy. Mount the relay as close to the pump as practically possible, have the shortest ground of equivalent gauge from the pump to the chassis, and use good quality sleeving and termination on everything.
'89 5.0L LX hatch: all 90mm 2.2L Blowzilla Dart Iron Eagle 306 @ 8.4:1, ported Vic Jr heads, TMoss ported GT40 lower, Deka 80# injectors, EDIS8, GUFB-A9L2-Moates tuned, Tremec 3550, 3.31 gears w/31-spline TruTrac
'66 GT 2+2 Fastback: carb'd 289, Canfield heads - EFI transformation pending
'71 Mach 1: totaled - R.I.P.