"So you currently have a pump
"So you currently have a pump installed, it just won't fill it for you?
Normally, a livewell/baitwell pump is installed at the transom (right through it to be more precice).
They come in a few different styles and gallon per hour (gph) ratings. All will normally fill your livewell adequately.
If the tank you are trying to fill is mounted high or far away from the pump (like a baitwell under the passenger seat) you may need a stronger pump than for other placements.
If your current pump ever worked properly, it's probably just shot and you could replace it with whatever is there.
I have a pair of 650 gph pumps, one for each of my 30 gallon wells - takes about 2 or 3 minutes to fill my tanks with that particular pump.
Places like Bass Pro, West Marine etc, sell "kits" to replace all the parts on a livewell pump system including the pump, strainer, hose, clamps - everything you could need...."