The net on the link is for a modern helmet and would not be correct for WWII helmet.
You can use the half inch knotted net as seen on the para on the left in your picture. There is evidence that this was used with the early Mk1 helmet (with the moulded rubber on the rim). You can also use the smaller hole woven net item as shown by your para on the right.
I am surprised you can not fit a net from a Mk II helmet on as I have transferred them between them before without a problem.
Are you in Denmark? if so I can only advise try the online sources like SoF or WPG who make repros of both types otherwise keep checking ebay. They are items you see at shows in the UK.
By the way have you got information on when that photo was taken as I am suspecting they may be Canadian Para's who are sometimes seen with jump boots.
Ramsey is correct in his suspicions, they are Canucks!
Sabre sales have the right sort of nets (and there is a bit of variety) I've got WWII nets with large and small weave and in brown, tan and green.
I personally use a small weave green net on most NWE lids, it's also no problem to change then between RAC/Airborne shells and MKII or MKIII
If anything MKIII shells are a stretch.
And yup, quite a well known picture of Canadian paras but I think even the majority of cannucks used ammo boots and gaiters and the Commonwealth deemed 'jump boots' a bit extravanagant and not much better than the infantry type.
The Brtish made a corcorran type jump boot very early on (41/42) when para units were being trialled but it wasnt adopted in the end.
"I think we are in rats' alley - Where the dead men lost their bones."