Looking for a unique and wonderful gift for the Children's Librarian in your life? Try tracking down some milk filters! Judging from some of the Google search results that bring visitors here, milk filters are harder to find than Sasquatch! Below I've compiled a source list for milk filters. Please note that I have not bought anything from the stores below and cannot vouch for them. I did not receive anything from the stores below for mentioning them. If you know of additional sources, please clue us in with a comment below!
Blain's Farm and Fleet sells a box of 100 15 inch milk filters (by KenAg) for $13.49 + shipping. You can input your zip code to get a shipping total. My zip code was $4.95 for economy shipping via the post office (within 5-10 business days).
Shane's Tack also sells a 100 quantity of the same milk filters for $20.97 + $9.08 shipping to the continental U.S. However, they do offer a volume discount (2 or more @ $20.34, 5 or more @ $19.71, 10 or more @ $19.08) that could be useful for those of you who work in a multi-branch library system or know other people who might want to "go in on" a bunch of filters together. For comparison shoppers, 10 boxes is a case of milk filters, sold for $204 at Giles Dairy Service. I was not able to get a shipping quote without creating an account.
If you are looking for a smaller sized milk filter, try True Harvest. You can get 100 of the 6.5 inch filters for $11.29 + shipping. A box was quoted to me as shipping for $6.93 via the post office.
If you live in Illinois, Wisconsin, or Iowa: there may be a Blain's Farm and Fleet near you. I believe the box I have came from the Woodstock, IL location (we have family in IL and my husband picked some up on a visit. Yes, he gets sent on weird errands sometimes).
As I live in an area of Michigan with plenty of farmers, you would think there would be a store nearby that sells milk filters. There is not. Apparently the farms around here use some sort of polyester "sock" to filter the milk. You learn something new everyday.