i need to get one for another application (ignition related), so (1) where are they available at - parts stores or just stereo shops? (2) are there different kinds that i'd need to figure out what kind i need?

 

The majority of noise filters out there are simply two coils. One coil excites the other via inductance and there is no physical contact between the coils. The theory is that they will break a ground loop by literally breaking the loop. Radio Shack carries the basic filter but you can get more newfangeled units elsewhere (stereo shops, etc).

 

Need more info in what you're trying do.
A ground loop isolator (like gummie described) would be inline with the RCAs and have no physical connection from the input to the output. A power line noise filter is a totally different animal need a connection from the input to the output.

 

this would be for an ignition coil power wire, actually. goes between the external coil and distributor (ignition) module. techs seem to think that will hopefully solve my issue.

 

??? What the 'issue'? Adding improper filtering here could leave you with other problems.