For the blocks, you might check out the listing at D&R Marine. They carry parts that work for DS. However, there are other places that sell equivalent blocks, so you might want to shop around.
http://www.drmarine.com/categories.asp?cat=64.
For the mainsheet block, there are different designs. There are those where the sheet has to be moved
down to uncleat. These can be difficult to use in situations where you want to work the sheet without cleating it. (The design is "self-cleating" which is not what you want when you are out in blustery conditions and need to dump the mainsheet at a moments notice when a gust hits).
You may also check out designs that incorporate a "ratchet block". (Alternatively you can replace one or more of the other blocks with ratchet blocks). A ratchet block will turn in one direction only, allowing easy tensioning, but resisting the line in the opposite direction - thus providing some (partial) holding power that makes it easier to hold the sheet without cleating it.
One flavor of ratchet block is the auto-ratchet. Here, the ratchet feature does not engage until there's a certain pull on the sheet. That way, you don't find yourself disengaging the ratchet manually in light conditions. I have one of those for the block on the underside of the boom right above the CB (Ronstan 55mm) works well for me.