As far as I can make out, the best way to find an agent would be to wait until this contract is fulfilled, see if they want more, submit any manuscript that the publishers are interested in to an agent, who, if they like the manuscript, would take me on and then deal with the publishers for me. I would not be interested in shopping it around, as I like the publishing people I work with.
Would this be the best way to go about it?
Your instincts are correct ... it would be difficult to find an agent for the contract you have now. This is for straight-up business reasons - there's no commission to be made on a contract that's already done, and none of us can afford to work for nothing.
If you're a published author with a second contract being offered, you will probably be able to find an agent without much trouble, but I don't think that's really the issue: what you're looking for is advice, not necessarily someone to negotiate for you. Which brings me to a small soliloquy on the nature of agenting.
Agents manage the business of writing so writers can get on with writing i.e. being creative. Sometimes agents are involved in the creative side - when writers ask us for input on ideas and manuscripts - but generally it's the business that we take care of. We give career advice, we sort out problems, we do contracts, we negotiate deals. You may not need any of these things - not all authors do. You may just need someone to answer your questions. You may wish to pay someone commission to answer your questions, and that's legitimate too. I suspect some authors have agents just so they have someone to talk to about their writing who is not a friend or family member; again, that's a perfectly legitimate reason to have an agent. But you may also find someone else who can answer them - a fellow writer who's been through the publishing process, or your local writers' centre. Of course if neither of these is available to you, an agent can certainly answer your questions and would, one hopes, be happy to do so. Getting published can be a confusing process the first, third, tenth time.
Here's another idea: ask your publisher, editor and publicist. Yes, they're busy, but it's their job to give you information, amongst other things. Sometimes those of us 'on the inside' can forget that people who are new to the publishing world don't know the same things we know. Sometimes we just need them to ask us and we'll be eager to spill. Go on, give it a try. If you don't ask, you don't get.