There are many consultants who can do this, but startups need to be realistic about what is newsworthy and what is not. A launch? If it's a great, innovative product, yes. A VC raise? If it's a notable amount of funding or the investors are well-known. A partnership? Rarely.
A great firm or consultant needs to be able to manage expectations with the client rather than promise constant press -- the latter is a red flag. In addition, the founders need to be willing to put in a lot of work as well. The startup is their story, not the consultant's, and the founders will be the ones who need to get out there and meet reporters. In the earliest stages, a PR consultant should be primarily a behind-the-scenes strategist (on messaging and branding) and a conduit for introductions to reporters. It needs to be the founders putting in the face time.
If you are a cash-strapped startup, my recommendation is to bring on a consultant to get press specifically for your launch or Series A raise. Having a firm on retainer can get expensive!
I'm happy to take a call if you want to discuss your options further.