Standard waterpump rebuild kits are available at lots of places, both on the web and in marine stores. If you need the pump cover and or pump base, these are not as available, and for your model (if you have flush port on lower unit?) you might need to visit a dealer.
If the gear oil has no water in it, and the pump cover is not scored, just grab a water pump repair kit and replace impeller, gakets and wearplate.
when I drained the gear oil from lower end plain water came out and after the plain water the gear oil came out and the oil did not appear to be deluted with any water. can that be explained?
Water in with the gear oil means a seal is bad. It may also mean damage to the gears and bearings. I recommend you purchase a waterpump base, impeller, wearplate and all gaskets. The pump base will have a new driveshaft seal, which is likely candidate for the fix for the leak. Clean up the driveshaft, and oil it so the pump base will slide on w/o damaging the seal. Use new orings and gaskets as well. Refill the gearcase and use new gaskets on the gearcase plugs.
Run the motor for a while(10 minutes or so), preferably in the lake, and then drain the gear oil. if it is clean, you likely fixed the leaking seal. if it is milky, you still have a problem.
If the gear oil is clean, carefully run the boat near the launch, in case the gears are bad. If it works OK, you have been lucky....