So, after taking advice on Bugman's Brewery forum, I've ordered some Wargames Foundry shields and I've just received them with an additional free (and lovely) viking figure:
Nevertheless, I'm not totally satisfied: the round Viking shields seem a little bit big for my dwarves. And the Norman Kite shields blister was a real disappointment. As shown on the official picture, they're ornamented with nice bosses:
So I'll see what I can do with the round ones!
ADDENDUM (on November 29th) Wargames Foundry has sent me a second set of blisters with bossed shields (for free!).