CP,

There a couple of ways you can do it, I've seen lowering plates you can get that lower the position of the rear shock using your existing shocks or you could just get lowering shocks.  Here's an example off US ebay:

http://cgi.ebay.com/ebaymotors/05-08-Harley-Sportster-adjustable-lowering-kit-CHROME_W0QQcmdZViewItemQQcategoryZ35569QQihZ012QQitemZ220262984243QQrdZ1QQsspagenameZWDVW

 

If you're not going for the "look" and you need it lowered because of your height you could try a different seat. Some seats are made for shorter people.

I have the Tamarack Machine Works 1" Lowering Kit on my bike. I went with taller shocks for more travel and softer spring rating then added the lowering kit to get my feet back on the ground; works well; easy to install; virtually invisible. About $70. Will fit the 883C. Mail overseas USPS no problems. http://www.tamarackmw.com/tamarackmw_054.htm
Alternatively you can get lower shocks, that usually gives you a firmer ride with less travel though... but you'll be able to go as low as 10" shocks (eg Licks has 10" shocks for the sporty) http://www.lickscycles.com/catalog/siteinfo.php?page_id=16. Will also mail overseas with USPS. You just tend to embed the footpegs and kickstand in the bitumen on corners
And of course anything from progressive in a shock lower than the 12.5" that you have stock will give you that look you are after. Since you have an EFI just watch your clearances between the tyre and the ECM tray under the seat (even worse if you have the deeper PCIII tray under there too) if you aren't buying direct from the dealer.
Or you might get "lucky" and pick up a set of stock take-offs from a Low or a Nightster on Ebay or in the classifieds. Just remember they took them off for a reason

Ooops My Bad!
Prices on the lowering blocks have gone up since last year... and you'll want chrome... with postage probably closer to $100.

Had my 1200c lowered for a while with progressive shocks but the problem you will have with these custom models is the belt guard will hit the frame when you go over bumps the nightster frame is different near the upper belt guard if your saw the picture that walka had of his bike in the competition the forum had his bike is lowered but he took his guard of i dont want to steer you away from it ,when mine was lowered i loved the look ,and to have both feet firmly on the ground is a big thing for short asses like me ,you could probably bend it or space it anyway see how you go cheers.

if your going to customise don't be afraid to customise !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Looks Good!