Minimal Pairs Resources

Hello,

I'm a Portuguese-speaking English teacher who teaches English to Brazilians and I've come across many pronunciation problems to which there doesn't seem to be many resources. I guess some of my students exhibit some unique pronunciation problems due to Brazilian Portuguese influence, I don't know...

Anyways, I was looking for a way to teach the difference between some minimal pairs, like:

/t/ vs. /tʃ/
In Brazilian Portuguese these sounds are allophones (the only word that uses /tʃ/ phonemically is "tchau", but this is adopted from Italian "ciao"), so my students sometimes have problems identifying the difference between, say, "teacher" and "cheater", or "sweet" and "switch".

/ɾ/ vs. /r/
Some students have a problem telling apart the flap/tap and the retroflex, even though they should be clearly different in Portuguese phonology as well. Many of my students pronounce "better" and "bearer" the same (both sound like "bearer" to me).

I've looked around the Internet and all minimal pairs sites don't include those pairs!! Are my students that unique??

Thanks for your help!
Radek