Peco Makes ON30 track with proper ties spacing and appearance and some switches.
I just did some searches. San Juan Car Company has a large line of ON3 and ON30 rolling stock built up and kits. They also have wheelsets to convert ON3 trucks and they have ON30 trucks built up. http://sanjuancarco.com
Also Labelle Woodworking has kits for ON3 passenger cars which would work on ON30 trucks.
Mainline Models used to have some very nice ON3 kits - you provide trucks and couplers. However, they have been bought out by someone, and I am not sure who. I think it might be Labelle, but it does not show up on the main Labelle web site.
Another good source appeasrs to be the ON30 Annual from White River Publications. It would probably have lots of ads for suppliers.