I buy stuff from a variety of sources. For exmple I bought unifix cubes off ebay a couple years ago. I was getting ready to use them again with my 3rd child, and found a math kit to use with teh cubes at teh local teacher resuorces store I frequent. I had activity cards to use with the cubes. I have often bought my manips at that store or at another teacher store on the other side of hte city. I also have a friend that runs a homeschool bookstore out of her home I buy a fair amount from. Otherwise I buy stuff from online stores, home science tools, canadian home education resources, etc
These are the materials that are out for exploration in addition to the curric we utilize
Math I use pattern blocks, unifix cubes, the 3 bear family, tanagrams, dominoes, dice and geoboards mainly for the early grades
Language arts tactile letters, magnet letters, salt or sand on a cookie sheet, a die from scattegories (eventually we lead up to playing the game but early on we just use the die and come up with single words), stamps of the letters, playdough(letter formation), a small white board and markers. As they get into reading not jsut letter I add letter tiles that snap together and reading rods, as well as sight word bingo
Science a scale/balance, magnets, magnifying glasses, colour paddles, mini cubes(I use centimeter cubes, I guess int he states they would be inches)-these are great for practicing mass and balance, bug catchers, I also make a tornado bottle with a simple tornado tube, and colour bottles etc, shells and rocks.
For all subjects I have a large selection of file folder activities that have matching games etc, file folder games and regular board games.