I use to make my own.I use to get two wheels (complete with tyres and rims) and get two pieces of four by four timber,square of the rims and sink the timber into the rims.Drill holes every two inches in the timber and cut the timber to height of about four foot.Get some jump cups and there ya gne set of upright wings.
For fillers, use old doors (normally peanuts to buy from the tip), or put a rug over the top pole , making a wall (my horse is scared of rugs unless he's wearing one!)