Look on eBay! I buy (and sell) oodles of used Schaefer blocks on eBay all the time. Great savings. Look at boat breakers too, like N and J in Wisconsin (Nick; a really good guy; he has loads of stuff). You will want a Schaefer 05-25 (fiddle) for the top and a 05-75 for the bottom (fiddle w/cam cleat/becket/swivel), rated at 7/16" line and 1500 lbs. These are as common as anything else anywhere. If you spend over $100 for the pair you got a poor deal. A set of new ones will set you back over $450.
Don't waste your money on snap shackles - not necessary or useful on a mainsheet. Only one has to have a swivel - typically the lower one; but some will insist it should be the upper one.
I'm assuming you have a traveler; if you don't have, you should have. And it should be in the cockpit, where it belongs, located at least 3/4 of the boom's length back from the gooseneck. Cabintop-mounted travelers provide less leverage (requiring more arm strength from you), impose a horrible load on the (cored) cabintop structure, and completely preclude the option of having a cam cleat on the lower block, so it has to be led somewhere else (unless you don't mind standing up to reach over the companionway to trim it each time).
Visit a good sailboat rigger and have double-braided low-stretch line spliced onto the lower fiddle's becket. I like my Yale cordage; but, again, browse the Web and
please don't assume Sta-Set X at WM is the only thing around - I am not a fan of that line at all. Sampson XLS is still the gold standard for performing-cruising boats of a certain vintage. And you can pick any color. (About 1.00/foot. You'll need about 44-48 ft.)
One
VERY cool trick is to rig the mainsheet purchase to have 'fine' and 'coarse' trim options. It'll require a cabintop winch, a halyard stopper near it, a cheek block on the deck, and two extra single blocks. Reeve the sheetline as usual, starting at the cam cleat, but instead of bringing the last end down to the becket, run it forward, along the underside of the boom, through the vang bail, to one block under the front of the boom, then down to the other one at the base of the mast (on center), then through the cheek block and back to the winch. Cleat it at the stopper and trim using the cam cleat on the traveler. When things get rough, cleat it there and trim it at the winch. Your boat is at just the right size to take advantage of this with '05'-series blocks and 4:1 purchase. We had this arrangement on our Raider 33 but with 6:1 (using then-brand-new very trick Harken ball bearing triples) and it worked terrifically.
But with just the two fiddles you'll have a durable system that will work just fine for you. Just don't understimate the values of used hardware! You sail a used boat now; don't you?