How to reference a button in a dynamic array

I’ve got a couple of columns of buttons loaded with attachMovie and looping through an xml array with a for loop, so they’re named, for example, “thisBtn”+i+"_mc". But I don’t seem to be able to reference them in the script with either a written-out name like thisBtn0_mc, or with “thisBtn”+i+"_mc".

How exactly do you reference each individual button?