Here is a list of superconductor suppliers:
Can superconductors (http://www.can-superconductors.com) is a Czech firm that sells different types of superconductors: weak pinning superconductors for Meissner effect, single domain crystals with strong pinning for trains and strong levitation, BSCCO bars to measure the resistance in four points . See the shop link : http://shop.can-superconductors.com/index.php
ATZ, a German firm (http://www.atz-gmbh.com) that builds prototypes using high Tc superconductors and that also sells disks with strong and medium pinning. Use strong pinning disk to make superconducting trains (diameter 30mm, thickness 12mm cut in two 6-mm slices to make 2 disks, with paraffin wax to enhance the life), use medium pinning disk to make levitation experiments while cooling (diameter 40mm, thickness 12mm cut in two 6-mm slices to make 2 disks, with paraffin wax to enhance the life).
Supermagnete to buy powerful magnets (http://www.supermagnete.de/fre). It is a bit expensive, but they have a lot of choice and are very responsive. Plus the estimate is quick, since the prices are written on the website…
Visit this site.
Visit wikidébrouillards.
You have to be with an authorized person in a professional context (high school, laboratory, university…) to have nitrogen delivered, for instance by SOS Azote or Air Liquide
