Vario is a brand name used by Lighthouse, which is a German commpany (Leuchtturm), so you ought to be able to find them easily in the Netherlands.
Lighthouse uses "Vario" for its 8 1/2 x 11 size pages.
Lighthouse uses "Grande" as its name for 9 x 12 (sorry, I don't know the metric sizes--perhaps the actual sizes are metric and the 81/2 x 11 and 9 x 12 merely are approximations) pages. They have Vario binders and Grande binders to fit both sizes.
Hagner and other suppliers have product lines that are comparable.
http://www.lighthouse.us/epages/lig...s/US/US_2203Lighthouse makes Vario pages with 4 pockets to a page, 3 pockets to a page, 2 pockets to a page, both see through and black background versions. The 2 pockets per page might be about right for smaller souvenir sheets.
An alternative, mentioned above is to use the larger sizes of Showguard (or equivalent) mounts. For instance, Showguard has 89 x 240 mm splitback mounts. Or 80 x 240 mm or 158 x 265 mm or 175 x 265 mm. These would handle a variety of souvenir sheets.
The other vendors of plastic mounts have the equivalent, I presume--I'm only familiar with Showguard sizes. One caution though, split-back mounts of this size can easily flop open when you turn a page that has a mount like this with a souvenir sheet or large block of stamps or cover in it. One can moisten a small corner of the second half of the mount (normally you only moisten one edge but leaving the opposite edge unstuck permits the flopping; stick that other edge down with a tiny bit of moistening and it won't flop but in order to open the mount and examine the sheet inside, you have to "unstick" one of the two edges).
That's one reason why I've shifted from using large Showguard mounts to 1 pocket, 2 pocket, 3 or 4 pocket Vario clear stockpages for blocks, strips, covers, souvenir sheets. Of course they also permit you to see both sides of a cover whereas Showguard etc. mounts do not.