Electronic tanpuras are recommended. These can be bought from India or online store of Radel / Raagini or Amazon.
Radel (Saarang Maestro Dx or Saarang Ranjani + 5 or Saarang Miraj Plus) or
Raagini (Raagini Digital, Swarangini Digital)
Strictly, phones or computers are not advised for practice
** Temporarily, you may use an online version (http://www.swarmanttra.com/category/download-mp3-tanpura-tabura-free/) or iPhone/Android free apps for generating digital tanpura shruthi
Ganamrutha Bodhini (Sangeetha Bala Padam) English.
https://www.amazon.com/Ganamrutha-Bodhini-S-Panchaapakesa-Iyer/dp/B000KGH4H6
http://www.amazon.in/Ganamrutha-Bodhini-Sangeetha-Padam-English/dp/B00JBJSYXQ
** Please make a durable cover for the book to protect it
Strings to use if needing to change them
#31- Talaam Strings
#30- Main String - Shadjam
#27- Second String - Panchamam
#21- DOUBLE WINDING - Mandharam
#19-12 - DOUBLE WINDING - Anu Mandharam