Anyone knows where could I buy those lamb slices for steamboat like where does the Suki-Ya lamb meat slices come from? Who or which supplier do they buy from? And yeah, I want lots of it with cheaper prices.

http://www.luckyfrozen.com.my/
http://www.tplfreshmeats.com/
http://www.leesfrozen.com/product/meat/

Theres plenty of them. If you're opening a business they can offer you better prices too. For one off purchase, some may or may not sell, in that case, just go to a butcher and ask them to slice for you which they usually do.

Thin slices like those, can only be sliced while frozen with proper equipment. Most good butchery has this.