Your 2000 9.9 Evinrude is actually manufactured by Suzuki. OMC had Suzuki start making their four strokes as well as some oil injected two strokes around 1998. When OMC went broke, Bombardier bought them out and they became BRP. Bombardier Recreational Products. Suzuki continues to manufacture many outboards with the BRP logo.
This link to a Suzuki Parts catalogue with help your cause. http://store.brownspoint.com/pdf/DF9.9_15(04-09).pdf
The oil drain plug is listed on page #5 part 6 engine oil regulator. As depicted it comes straight off the bottom of the engine block. It is neither visible or accessible without removing the side cover. Pg. 58 part 3
When standing at the rear of the engine facing forward you will need to remove the left side cover.
Any BRP, Suzuki or Johnson/Evinrude dealer will be able to locate a filter for you. I'm not sure if an an Automotive supply can cross reference it or if it is a dealer only item.
The filter and drain plug on my Suzuki dumb ass 25 were almost identical. They utilize a cardboard cartridge encased in a seperate metal housing. It is most important tha the gasket betweem the metal housing and the block in in proper position when replaced. If not the a serious oil leak can ocurr and can go unnoticed for some time.
When I had mine the only outboard with a spin on/automotive style filter were the Hondas. This may have changed.
Good luck, Roe Bag.