Hi,
Transconductance OpAmp are available in Farnell or RS components, you can get plenty of them. One interesting feature is that their bandwidth is much higher compared to the ordinary voltage feedback OpAmp. You can create easily adjustable low pass or high pass filters with them. If you need narrow band pass filter you need to use combination of low pass and high pass filter.
But I agree - they are not widely used and you need to learn how to work with them.
Kind regards,
Luben