Is it standard to "pitch" gallery/museum exhibition ideas?

It is so common that museums have policies for submission that you can follow. Just contact several of them. I suggest that a photo or art gallery would be a more likely place for your exhibition.

To get an exhibit, you will probably have to prove to the museum that your idea will attract enough visitors to the museum. Of course, you will be in direct competition with other exhibits. It is also important to know that certain museums only accept certain types of exhibitions. Given your description, you should probably go to a photo or art gallery, like @YARNLADY suggested.

Galleries and museums are different animals.

Museums, even contemporary art museums, generally require the exhibition to have some degree of historical value, or a bold statement about modernity.

Galleries are wide spread in their requirements, and many specialize in particular mediums. A sculpture gallery isn’t going to be prepared for a photo exhibition.

Is it a top tier gallery? They’ll only show artists that have attained some degree of fame with a long list of past exhibitions under their belt.

If you don’t have past exhibitions under your belt, then presenting an idea won’t carry much weight. You may need to produce the work, and then shop it around, or have it tied to a publicity campaign to get attention you seek.

Photo exhibitions are often found in eclectic neighborhood photo studios that throw monthly parties and exhibit out of town photographers. They’re also seen in many coffee shops and speak easy’s, martini bars. No curator means open standards. Photo exhibitions are also very popular with the art fair circuit. But the best fairs have strict admission requirements and charge fees to participate. Those who make money at it have a routine with traveling gear and display mechanics worked out.

Art is a business.

At art school one of the less exciting things we had to learn was how to write exhibition proposal’s for galleries. So yes, it’s normal. Though I expect you’ll need more than just a written proposal if you don’t already have a reputation or rapport with the gallery. I’d provide useful visual aids and/or images of your past work if it can help the gallery folks visualize the show you want to put together.

If you can you ought to include an artistic resume including previous art shows you’ve been involved in and direct them to your website if you have one for your art.

Exhibits have been pitched to museums. Often by other museums who want to travel their exhibits, but not always.

When I worked at the Navy Museum in Washington DC a woman walked in with an idea for an exhibit for which she had done research and had taken pictures. It fit into our mandate and so we did it and she curated it. It is possible.

If you are trying to sell your photos, though, a gallery is a more appropriate venue.

At the Smithsonian American Art Museum [where I also worked] things were “pitched” on a much less informal level as the curators were more actively seeking to develop exhibitions themselves.

Do you know any of the curators of your target museums?