Google with the words Maple bookcase---and use the Image section of Google.

You will see what this light colored wood looks like and how it can be stained.

Most furniture today is made using plywood for large flat pieces. Lumberyards---real ones, not Home Depot/Lowe's/Menards/etc.-----carry or can order any kind of hardwood plywood---maple, oak, cherry, walnut, or even exotics.

Consider purchasing bookcases and then having them permanently installed.
You can apply trim to the front where the units meet to hide the joint, and the price is a lot cheaper.
Even if you had to have them cut down in width or height top get a good fit.