Although you're asking specifically about following up here I think your have a much broader issue facing you that you'll need to deal with. You taking the initiate to follow up is great, but if your outsourcing company isn't putting out the effort to find your next engagement you have bigger fish to fry.
First off you don't indicate if you are in a contract role (i.e. no pay while on the bench) or in staff role (i.e. paid bench time). The distinction is fairly important because it does effect how your company approaches placing you.
Obviously if you're in a staff role and being paid for your downtime the company has made an investment in your career, so they are more apt to quickly place you in another project or use your skills for other task such as interviewing, assisting with prospects that fit your technical knowledge, or evaluating potential projects.
If you're purely a contractor then obviously you're losing money while on the bench. And although your employer isn't making its cut they certainly aren't shelling out cash for you to sit around the house.
Many consulting companies are well known for promising the moon as far as their need for your skills; not only on the current project but on future projects as well. Despite these promises a great deal of those companies are only concerned about the current project or requisition, regardless of what they've told you in the past.
If they are not putting out the effort to place you then they are clearly indicating that they either don't have a need for your skills, are not satisfied with your history/performance, or are simply being short sighted. If they really wanted to keep you in the stable you'd be hearing from them every other day or so even if it was only to say they haven't found anything yet.
Either way I'd suggest you start looking at other outsourcing companies to partner with. When doing that I'd ask specifically about the average bench time for their stable.
Although I'm sure this isn't current I've read before that a 30% bench/down time is very common for consultants. While my experience with one company in particular was less then 1% bench/down time over the course of seven years.
Obviously your mileage will vary.