You don’t need zips to attach side pouches to a Munro - I’ve attached them to mine before using the compression straps. The replacement (Centurio) comes with zips as standard.
But neither is really a bergan replacement - they’re daysacks for daysack-sized loads.
A second-hand infantry bergan and a decent daysack is still going to be your best bet and by far the best value solution.
Those things that I couldn’t fit in the Bergen would probably be the stuff I would need day to day and stuff that I would be putting in a daysack - ie. stuff that I would keep in the pouches and use with a jetpack yoke!!!