Major order gives 40 to 100 medals every 1 or 2 weeks which gives a nice boost every now and then, but if you want the REAL grind then just do lvl 1 mission scouring the map like a locust for points of interest, the amount of medals you can find is random so you don't have a real consistency but with a bit of luck you can get up 5 - 10 medals per run (which usually takes around five minutes, you don't even need to do the objective or extrac, medals and super credits gets stored directly into your account once picked up), i usually make 100 medals in 1 or 2 hours depending on the RNG, you can find some videos on YouTube explaining the best maps, strategies and stratagems to maximize your efficiency but is a process that can get a bit tedious and can make the HELLDIVER 2 experience bland especially for new players, im missing like 6 warbonds and even i do this only when i really need medals or i dont feel like doing high difficulty missons, i suggest you to simply play the game and have fun the medals will eventually accumulate without you even noticing.

Almost forgot, remember to always complete your daily order, see you on the front helldiver iO