its not cost effective to deal with them with infantry as they are designed to be anti inf. An mg might make them retreat, but if they pop smoke or you make a mistake you will lose it.
vetted pgrens and vetted grens with lmg/g43 and flamer pio can do damage but will also die quickly if not in cover or get grenaded, your best bet early on is to use flamer half track
Shocks are the ultimate infantry based anti-infantry. You can beat them with good micro, mgs, and snipers, but you should really get out some sort of armor to really counter them or you'll end up losing more on average then your opponent in engagements.
you gotta use mgs and vehicles or they'll just run through you. Bunkers also help as well. I find not giving them easy targets tends to discourage people from spamming buttloads of shocks so when I do need infantry im not facing 4 squads . If you see a shock spammer hold off on pgs and keep grens to minimum, go snipers/mgs and use grens just for pfausts and mg screen.