This is a great question Lindsay. I have had quite a few project only clients. I was just talking to a friend VA of mine about this same subject. One of the reasons that clients choose a VA is either:
A) it is there first time and they really do not know how to use a VA,
B) they are on a budget and can only afford small project rates
C) They are testing your skills as a VA to see if you will work out for a full time or part time VA for their specific needs. I personally have found that the above is the most common.
To target your "ideal" client go where they are online chatting or off line meeting.
Take time to view their site and target specific needs you find they may need. For instance if you are targeting Real Estate Agents then join the groups in your area that they are likely to join.
Send them information about what you can do for them to save them time and $$$.
Get involved with their Charters, Networking Events and online presence.
The more you learn about your ideal client the better prepared you will be when they start asking you questions.
Andrea~