I'm a little biased but if it's anything like my LVOA I reckon you wouldn't be disappointed with this beast... https://www.patrolbase.co.uk/krytac-mk-ii-trident-lmg-enhanced
the l86 or m27IAR type would fit the bill, but as this is airsoft you could just get a drum mag for an m4....
Yup as the guys have said just get what ever you fancy and as long as there’s one available for it just stick a boxmag on it .