Many blocks have bearings that do not need grease. Generally, you don't need a metal sheave unless you are running wire through it. Wood, although pretty and nostalgic, is not as durable or as light as the metal or synthetic blocks.
To answer your question, I would look through the catalogs of the major block manufacturers. Harken
is the first one that comes to mind. Many blocks, especially the more expensive ones, can be disassembled.
For the cheaper blocks, once the bearings and raceways wear out, its cheaper to buy a new block anyway. That's why they do not make the inexpensive blocks repairable...I'm sure new replacement parts
would cost more than a new block. Plus its more expensive to manufacture a block that is repairable.