Here's a great retrofit option - Green Creative's Innofit Series!
Designed and engineered for retrofit or new construction installation and features adjustable lumen output for three distinct lumen levels equivalent to various CFL lamp combinations. The CDL is universally compatible in existing architectural and commercial housings and features easy-fit installation with adjustable spring-action housing clips. You don't need a housing!! Now you get LED lighting and energy savings where you need it.
Comes in 4", 6", 8" and 9.5" sizes. See details here and call GLG for pricing!