B, C, D, F, G, are very rare in Finnish, usually they exist in some loanwords
Q, W, X, Z doesn't exists but are in the alphabet for compatibility reasons
Surprisingly also Ö is rare while Ä is not.
However, these are very common in quintessential Finnish words:
A, I, O, U, E, Y
Very common consonants are L, N, S
Common double-consonants are KK, SS, TT
These are loanwords which are using the foreign letters instead of trying to change these words into more Finnish like:
-abi -abortti -absoluuttinen -bakteeri -banaali -behaviorismi -cocktail -city -college -data -dealer -desantti -ego -fenomenaalinen -fenotyyppi -festari -glögi (interesting for its using foreign letters and also ö, it is Swedish loanword) -gospel -graniitti -magneetti
You wont find many words using these foreign letters
p.s. I just browsed through a dictionary and about 4000 words start with A
