If the upside is what you indicate it could be, you should consider starting a C corp.

The Sec 1202 improvements in the OBBB make C corp very attractive to start over the typical default of scorp/llc.

You could find any number of middle market banks with sell side advisors/third party partners. You'd have to pitch them since there is no history or familiarity with what you're trying to start. It will feel like a dog and pony show and you're the attractiion.

I would start with a short pitch package and just try to connect with different banks you might already have a relationship with.

I'd probably also consider starting legal upfront for what you want the deal structure to look like. That will make the negotiations easier to where they know your starting point rather than just exchanging redlines for 3 months when you'll never come to an agreement. That's a waste of time.

Sims advice was good.

Private Equity is an expensive way to fund the business, and they often take a much more active role in management of the business that can leave you as the founder on the outside looking in, but if they have a partnership team with experience in your product/service space or connections (think future customer ties) that you can leverage it may be a reasonable route to pursue.