I know it isn't a new idea, but I'd like to show my next model crossing railroad tracks. Are there ready made diorama bases I can use or do I need to source model railroad materials and make them myself?

Trumpeter sells a box of plastic track . Model Rail Road Shops used to sell single pieces of 3 ft / metre length large gauge metal track and basswood ties . You can stain the ties any color you like and blacken it works on the rail.
Try to find 1 Gauge track and ties as its close to 1 / 35 scale ( 1 / 32 - 54 mm )

Is this along the lines of what you are looking for Bill?

"The Crossing" by Great North Roads

Thank you both for responding. I'm not sure whether I want to make the base from scratch or pick up something from a vendor like Great North Roads. Jeremy, you read my mind ... I was looking at that base (as well as a few others). Need to contact the company, though, as a lot of the products don't include dimensions.