Although you can purchase beads, tools, and other supplies at Ben Franklin Crafts, JoAnn Fabrics, and Walmart (Walmart has a good 3-plier kit for less than $10), I have found a number of good places to purchase other rosary supplies, especially the other hard-to -locate items like rosary centers and saints medals.
For beads and other things, you can get many from thrift shops, rummage sales, ebay, and your own attic!

Here are some good links for supplies:

1) Eyepins: get this silver color one: http://www.pandahall.com/wholesale/eyepins/11188.html . Panda Hall is a good site for beads and other things, very inexpensive, but since they are coming from China you may have to wait 2 weeks or more for arrival.

2) Saints medals and crucifixes: Catholic Prayer Cards - http://www.catholicprayercards.org/CatholicSaintMedals.html?OVRAW=saint%20medals&OVKEY=saint%20medal&OVMTC=standard&OVADID=8750602022&OVKWID=72756867022

3) Rosary Centers: Discount Catholic Store has a wide selection: http://www.discountcatholicstore.com/rosary_centers.htm

4) Beads: www.pandahall.com , www.firemountaingems.com, www.ebay.com, and many, many other places.