Ok, what do u think is the hard counter for SU76?
Im always talking bout MORE than 2 SU76, nobody builds just one of them.
Pak wall is a really good counter that comes early. One pak is not a hard counter becouse of barrage, but more of them, well positioned and spaced out, definitely are. For additional buff you can support your pak wall with reinforcement ht or command tank. Other hard counters come later, as they should in a well designed rts. These are generally tanks with either better range or armour that su-76 has hard time to crack. So the best counters are obviously JT, Ele, pak43, but if you dont have the commander, panthers should work as well. If you find panther to have too little DPS you can always use its armour to lead the charge and support it with some stugs. If you manage to catch su76 without infantry support, or you just managed to retreat his blob, then all kinds of shrecks and other handheld AT that you may find is really good vs su76 - it can barrage only once so it has no chance against moving infantry. And last but definitely not the least, the mighty stuka AT support.
As you can see, there is plenty of options.
Do also mind that su76 without su85 or infantry support has no spotting so effectively cant use its 60 range. If you happen to find a situation when they suffer from that, you can close in with the stug, or more than one if they have a lot of su76s, and easily kill it as well. I don't count it as hard counter as it is situational but it often works really well - you just need to find the moment.