You need to match one with the same DS voltage rating, same gate polarity (n-channel), same enhancement mode, same package. Then choose the lowest rds on spec that your willing to pay for (but not higher than the current ones)
Sounds like a difficult task but it's not at all. Go to an online seller (I use RS online) and use the filters. It'll narrow your search from thousands to just a few to choose from.
I'll try and find the part no.s for the ones I ordered for my kt controller.