Be patient, but don't give up on them.
People are busy.
In the real estate business, we would LOVE to be clerking and just write up a listing or a sale with each customer that comes to the counter. Our business just is not like that. It can take months or even years for some clients to act.
An occasional call, Email or card can let them know you are there when they need you but you are not going to harass them all the time.