I have a power vent LP water heater and have recently gotten natural gas to the house .The manufacture says it can be converted but I may have trouble finding the parts do you have any suggestions ?

Call gas company, they may very well convert it for you.

Google " convert water heater to natural gas"
See
http://www.rheem.com/docs/FetchDocum...c-b7c7a4a1d137
You will probably need to know the make and model of the gas valve, not make of water heater. Its on the gas valve.

Many places sell conversion kits, Lowe's for one, depending on brand.
All else fails call plumber.

There are kits for most hot water heaters to change types of gas. The kits have two parts: a new orifice and a spring or spacer to change the resistance of the diaphragm in the gas valve. Some gas valves simply turn over a part on the top to change the gas pressure.