Your best bet is probably to come to Japan on a tourist visa first and then look in newspapers and magazines for openings, or just stop in at bars that seem comfortable to you and ask about openings.
A lot of hostess bars pay under the table and don't require visas, but in that case you'll have to renew your tourist visa, or leave Japan regularly to get a new one. Some clubs do offer visas, but recently Japan has increased restrictions on issuance of entertainer visas, and it may be more difficult to get one this time.
Good luck!