Agree with all of the above responses. Bear excursions - the ones specifically designed to see bears - are timed to the salmon runs in particular areas (typically mid to late July and August). The operators know they bears will be at certain rivers and streams and that's where they take you. The salmon can be so thick in the river, it's really a sight to see. If you had a net, you could just scoop them up! Bear paradise.
All that being said, the bears are still around other months, just not as likely to be concentrated in one particular area. You may very well see bears (I've read lots of reports of people seeing them at Mendenhall, though we did not), but you may not. I do think that the further you get away from the port towns and out into the wilderness, the better chance you have. There are so many other things to experience in Alaska, that I don't think it will impact your trip too much either way. As you noted, sailing later wasn't an option, so I wouldn't worry about it about it and just enjoy the amazing things you will see!
Edited to add: We used Island Wings last summer for a bear excursion. They were great to work with and communicate with before hand about choosing the right tour. While they might not be offering a dedicated bear tour when you are there, they offer plenty of other flight seeing tours, and they should be able to tell you if they have one with at least a decent chance of seeing bears. It's worth a try anyway.
