Welcome to the forum.
According to M. Swan's Learner English, p115, your students are not unique, if this can be of any help. Unfortunately, he doesn't offer any ready-made recipes. The most common 'set' of resources usually consists of::
English Pronunciation in Use
Sheep or Ship? and its online minimal pairs practice
On-line are available:
Minimal Pairs /?/ and /t/
Minimal pairs for English RP
Extended Minimal Pairs for English
and obviously many more
My favourite, however, is A. Underhill's Sound foundation and the application available for free.
Hope, it could help
- For Teachers