Hello,
We are happy to hear you are interested in furthering your education with TDI!
We apologize for the current state of the online store, we are in the process of updating it, and the new system will be online VERY soon.
If you have chosen an instructor/facility to work with, I would suggest getting in touch with them and see if you can purchase materials ahead of time.
There are also several online retailers that you can order materials from, here's a quick list to get you started:
Training Materials : Dive Addicts Inc
Technical_Diving
https://www.divegearexpress.com/tdi-manuals
Please let us know if there is anything else you need, and enjoy your courses!