Congratulations!
I'm not sure what size/lengths you are looking for, but here is what I have found out. Since maternity fitness wear is generally more expensive (with less selection and less sales) than "regular" fitness wear, I chose to size-up with pants that have stretchy waist bands and/or are low-rise. Kohls.com has alot of cute, inexpensive junior activewear pants with varying inseams (31" to 34") that work great (if you are generally smaller in the hips) because the waists have quite a bit of give that you can grow into. I could buy 4 pairs of "regular" pants for what I paid for 1 pair of maternity pants. I don't know about misses fitness wear, but I'm sure that there are also some pants with the lower rise and stretchy waist that would work good too.
As far as true maternity fitness wear, FitMaternity.com told me that all of their pants' inseams are 30", which is way too short for me. DueMaternity.com has some cute black yoga pants. The Ripe brand has a 33" inseam. OldNavy.com and Gap.com also sell activewear. The problem that I have is that I have a long inseam, so finding maternity pants long enough was my problem, which is why I opted to use "regular" sized-up clothes as my fitness wear.
Also, if you are looking to extend your pre-pregnancy pants, the Bella Band works good.
HTH!