Best bet finding suitable meats is to get a card to Kespro and Metro-Tukku, they stock more meats than most places (since they sell only to companies).
Kespro might have skirt steaks since they sell IBP Tyson meats imported from USA. They definitely have flank steaks. Be prepared to pay a hefty sum compared to USA prices, though.
Also, there is a company called Baron's Food situated in Turku, although their meats are located in Helsinki. They have pretty extensive stock list available as PDF
More large scale meat sellers: Heinon Tukku, Lihatukku Roslund, Lihatukku Tamminen, Chef Wotkins.