The upcoming new amiibos which went live not too long ago have already been sold out on the UK retailer ShopTo. But there's always a chance to pre-order them off Amazon UK when they're listed plus they're cheaper (ShopTo's £14.86 while Amazon's £10.85) and are sent in secure boxes just like ShopTo.
Squid amiibo in Europe/UK is an exclusive to the Special Edition bundle that includes the amiibo and game:
P.S.: I have pre-ordered every single one of the amiibos listed but ones such as Splatoon Boy & Girl and the Jigglypuff amiibo I think I'll cancel or sell to someone who wants it.