Would like to read some books about siddhars - appreciate if you can recommend some
One such book in tamil is Sathuragiri thala puranam available at thamarai prachuram
In THAMARAI PATHIPPAGAM, Vadapalani, Chennai-26, They publish around 40 to 50 books, all related to siddhars.
Hope you will be pleased with the collections over there.
In Tamil, by far I know, they have very good collections.