There appear to be no aftermarket retro fits for the LATCH system however, there are people that have done DIY installations though.
If you look at the latch system itself, its just three loops that the seats clip into. It should be fairly easy for a handy DIYer or mechanic to do. I do think most mechanics will NOT do this as it opens up a huge liablity should your child get hurt due to a failure of the homemade system.
There are adapters though:
Century/Graco EZ LATCH ™ Model #8405. This is the newest EZ LATCH kit from Century and will eventually replace the original #4025 kit (see below). This new version is compatible with most Century AND Graco carseats manufactured after September 1, 1997. See:
Graco EZ LATCH #8405
DO NOT USE this kit with the following Century models:
Avanta: 41500, 41530, 41540, 41570, 41580, 41640, 41650, 41670, 41672
Encore/Ovation: 4612, 4613, 4615, 4616, 4617, 4618, 4619, 4632, 4633, 4635, 4636, 4642, 4643, 4662, 4663, 4665, 4666, 44612, 44615, 44617, 44618, 44635, 44643, 44662, 44665.
Smart Move: 4709, 4710, 4712, 4714, 4720, 4724, 4735, 4750, 4765, 44709, 44710, 44712, 44714, 44765.
Bravo (DO NOT use in REAR facing mode. USE forward facing ONLY): 4620, 4621, 4670, 44620, 44622, 44623, 44630, 44631, 44633, 44670.
Also, DO NOT use this kit with the Old Graco Snugride ™ Base Model (#8411, knob recline adjuster). This kit CAN be used with the New Graco Snugride ™ Base Model #8403, #8412 (3 position tab recline adjuster)
Century EZ LATCH ™ Model #4025 (Discontinued). This is the original EZ LATCH kit from Century This version is compatible with all Century carseats manufactured since September 1, 1997. It is NOT compatible with Graco carseats or bases.
Cosco LATCH Belt Retro-Fit Kit Model 02-A01. This kit is for Cosco, Eddie Bauer and Safety 1st car seats made in or after 1995. You MUST have a top-tether to use this kit with a forward-facing car seat, and it is for use ONLY with car seats that have an internal harness or shield. It is not to be used with their car-beds, shield boosters, belt-positioning-only booster seats or travel vests. It is not for use with the Maxi Cosi Priori, which was distributed by Cosco/Dorel. See:
Cosco 02-A01 LATCH Retro-fit Kit
Evenflo SecureRight ™ LATCH System Retrofit Kit Model #630050. This kit will work with many Evenflo booster, convertible and infant car seats. Though not listed in the manual, it may be preferable to use only Evenflo seats made since September 1, 1999, since these models include a tether which should be used with LATCH. The following is a list of compatible products listed on the product box or in the manual:
Infant: Cozy Carry, Discovery, First Choice, On My Way (WITHOUT BASE ONLY). DO NOT Use with ANY On My Way Base.
Convertible: Champion, Conquest, Horizon, Medallion, Odyssey, Scout, Secure Advantage, Secure Choice, Titan, Triumph, Trooper, Ultara
Booster: Apollo (WITH HARNESS ONLY), Express (WITH HARNESS ONLY)
Columbia Medical has a LATCH retrofit kit available for its Model 2000 Orthopedic Car Seat. Snug Seat has a retrofit kit available for its Gorilla Seat Postural Seating System. Please contact the manufacturer for details.
Again, with all these products, please contact the manufacturer for the current list of compatible carseats, as these lists may not reflect recent updates or changes! LATCH retrofit kits cannot be used as a restraint directly on a passenger. The use of a LATCH retrofit kit on another brand or model that is not listed in the manual may result in an unsafe configuration. Even though it may appear to work well, it could loosen over time or fail because crash forces will not properly distributed.