Check the sportsbooks listed in this section, you'll surely find a lot. I think most sportsbook has a welcome bonus as that is already a basic marketing strategy to attract bettors, so go check and you shall find. Tip, check their profile to know if they are reputable.
Have to be careful with this advice OP, remember that there are gambling sites listed in this board that are having issues, accusations and evidences that they are scamming people like 1xbit so tread carefully if you plan to do it the right way.