You can buy thermoelectric modules from professional electronics catalogs and consumer sites like Amazon or Ebay.
Bulk thermoelectric modules are cheap and plentiful on Alibaba.com, and you can ask for custom models to be made to your specification. Here is a page from Alibaba for the TEC1-12706 like in the datasheet from Part 4 of this tutorial: https://www.alibaba.com/showroom/tec1--12706.html
Read Part 8 of this Tutorial - A Starter Project: https://www.collaborizm.com/thread/Bk5_6aaub
To see a Collaborizm project using thermoelectric modules, check out Cool India: https://www.collaborizm.com/project/SJVLyK2uZ