This could be a tough order and the best way to approach this is to work with a broker who will help you target properties that match your needs. If you are working with the right agent they would be on the look out for properties that match your needs and may even know of some that are not listed in the MLS.
In addition if you have identified a building that you want to live in your agent can mail the building looking to see if anyone is interested in selling their unit on the market. You need to find an aggressive buyer's agent especially in this seller's market.
The other option is to expand your search into other communities like Somerville, Boston, or maybe even Chelsea.
I am sure you can find him online.
Generally speaking, It's difficult to find historic lofts in Boston/Cambridge. My suggestion is chase the architecture and be open to where you live (I.e, go look at all the historic lofts on the market in the various neighborhoods and then see how you feel). Unfortunately, you may have to be flexible on where you live to get that perfect incredible space.
Other places to consider are: the Leather District (the historic loft conversions here are a personal fav'), the North End (specifically the building on 120 Fulton street - converted elevator factory - rare to market but spectacular), brewery lofts in JP, some buildings in the Seaport District, and Aberdeen Way in Cambridge was a great loft conversion done a couple years ago. Plus there are these amazing artist lofts in Central Square on Brookline Street. They rarely come on the market but there is one right now.
The alternative is that you buy something with historic charm, get a contractor who does this kind of work and design your own loft.
Here are some good examples:
Great price per square foot:
Here are two you could play with:
Brookline Street loft, central square -pic's don't do justice:
Here is an interesting alternative in Beacon Hill - similar floor place as 305 Cambridge, perhaps not as much industrial charm?:
This awesome one is in South Boston and has tons of historic architectural detail:
True Leather District loft:
This loft is another personal favorite that just had a huge price reduction - the developer did an incredible job. The location is awesome and the interiors are great (pictures don't do it justice ):
"Would it be reasonable to talk t a developer that could find a building an convert it?"
I think you'd be spinning your tires going about it this way, plus you're adding years to your timeframe, especially if you're talking about developing an entire loft building.
You have a pretty specific search, and you can only play the cards that you're dealt.