Welcome to FTE...And hey, don't worry about asking dumb questions, it gives all of us the opportunity to use up all the dumb answers we have (which run about 10 to 1 against the goos ones).
You shouldn't have too much trouble find ing a set of decent rear fenders for your 51/52. But, here is a stranger question. Are you sure the fenders are just 53 or is the entire bed off a 53-56 series? It would actually be easier to mount the whole newer bed than just the fenders because of the length of the fenders off the 53.
Also, something to know is that most of the parts off the F1s are interchangeable from 48-52. BUT, Ford chanced the design of the bed in late 50 (maybe 51) from the stamped side to the flush side. So if you have a flush sides short bed on your truck, only rear fenders off a late 51 or 52 will work - the earlier ones had notches to fit the bed wont work.
Also, F1 fenders were 2 1/2 inches wider (each) than those from the larger trucks because the long beds were wider.
If you go on ebay on sunday after 7pm PDT, the guys parting out trucks usually post all their pulls from the weekend. Some guys will list a lot of parts which tells you they are cannabalizing a truck. If you see a lot of parts but not fenders ask them if they have any or will have any soon. Chances are they do but are just not listing them because of shipping costs or the like.