What would be a good source for the blocks?
You can buy them pre-made - for example, Columbia Games sells them at prices which will look very reasonable if you ever try and make your own. SpielMaterial sells them. Print and Play Productions sells them.
You can buy existing games which have blocks in and repurpose them. For example, I came across some cheap copies of Skyline 3000 in a UK clearance shop and bought them for the bits.
You can make your own - if you can find strips of beech or another close-grained hardwood which already have the right profile, then a mitre box, a clamp for a stop-block (to ensure all blocks are the same size!) and a tenon saw or similar will be all you strictly speaking need (although a bandsaw or table saw would be better). Use a sanding block or a stationary disc sander to clean up the sawn edges, and paint. Weirdly, after a lot of experimentation, the best paint I've found for wooden game pieces at home is paint markers - Uni Posca and the like.