In Music Creator LE 5 there are many categories under the instrument selection that don't have anything under them. For instance Analog Sweeps under Synth has nothing in it. So is there some way to get more?

is this in the Cakewalk SoundCenter?  if so, I imagine they only gave you a few sounds to get by with for the LE version.  you'd need to upgrade to the full MC6 version to get the full sounds that come with it.
 
also, there are some add on packs you can buy in the cakewalk store for the Cakewalk SoundCenter - but I'd still recommend getting the full version of MC6 FIRST because it adds a lot of basic sounds you don't have yet.

If you're looking for something for electronic dance music, there are loads of free synthesizers, drum machines etc. which have a lot for you to dig in. 
www.kvraudio.com is a place to look for both free and commercial stuff.

Yeah, even the full version 6 I think has 150 or so instruments. You can add more with the add on paks.
 
When you add the paks, the instruments in them drop into the correct places in CSC.

Lots of reduced CSC expansion packs on Steam now! Just picked up the Mellotron pack - prog-tastic.

SO... the LE versions usually are free and bundled with some other software.
 
Buying the full version of MC6t gives you a lot of sounds..(150 or so IIRC) ..and looking at it this way, the deal is worth picking up just based on the cost of the sounds you are getting in the basic package....it's still like you're getting the full version of the DAW for free.
 
Then simply keep an eye on the store for "sales" which they do run from time to time and the the prices get even better. Last time I looked that had a super no-brainer deal on MC6t.... I think it was like $20 or some insane price.