Well, here’s the rules for shields, with approximate sizes…polearms are on the same page.
https://www.profounddecisions.co.uk/empire-wiki/Weapons_%26_armour#Shields
and this old thread on making orc kit:
Some of the groups in the Imperial Orcs have their own shield designs, and it may be worth talking to them and seeing if they have any spare or available, if you want to join their groups.
Bear in mind that if you want to get extra hits from your armour, it’ll have to be a bit more cohesive than torso + helm, but not by much 
There are a lot of suppliers listed on the Empire wiki:
And most of them will be at any one event. If you’ve the money, you could likely acquire all the kit you want in an hour or so of shopping on Friday afternoon, before time-in That’s weapons, shield, armour, and “soft kit”.
I suspect that there’ll be a few experienced orcs along to give some specific advice, but as general guidelines:
Do your best with kit, you won’t be the best, but you won’t be the worst.
Go for warm and comfortable over in-character. Especially re boots. Heavy socks and waterproof boots are essential for event 1 each year. Maybe some thermal underwear as well.
Charity shops are good for finding all manner of things, which can be made very IC and nation-specific with a bit of crude/primal embroidery, some designs painted on, extra dangly bits, and so on.
And welcome to the forum and the game!