On the left there is a search box. Type in a hashtag and it will give you a list of possible hashtags. Click on one of them and the search results come up in the right-hand column.

Your instance may vary, but that works on mine, and is effective.

Either that or follow a few people and then see who they boost. Follow those boostees if they look interesting. Growth is slower and more organic, but it's a good way to keep growth under control and not end up with a firehose.