Unless you have a few combat ships in there...many HRPs and many Shield Boosters can drain mats very fast...thankfully we have mat traders
Personally I wouldn't mat grind...play the game and any mats you come across, either from POI or combat, just scoop them. Before you know it you'll have enough for many maxed out G5 upgrades.
Take a trip to crystalline shards, as others have mentioned, as you can fill up the top level raw mats from 0 to max at a single site without logging...Quick Guide on this:
(1) Guide / Tutorial How to fill all of your Raw Materials bins using Crystalline Shards. | Frontier Forums
Doing it this way enables you to experience many aspects of ED without a grind. I've been playing since alpha and I never have maxed out all my mats...there's no point. All my ships are full maxed out g5 but I've never grinded for mats, just played the game.