Parts are still available for the Javelin from D&R Marine,
www.drmarine.com
The Javelin CB weighs about 49#, but is still a centerboard, a typical "retractable keel" fro a boat that size would weigh 2-4 times what the Javelin Cb weighs.
There are a lot of 14-16' centerboard boats on the used market, if you still want to replace the Javelin, a few that come to mind are the Catalina/Capri 14.2 which has the option of an outboard bracket, the Newport 16 (aka: Gloucester 16) is another good little boat that even has a small cabin, she actually does more or less have a retractable-keel (weight about 200#) and so will be more stable than a Javelin, you can clamp an outboard right to the transom, just like on a Javelin. The ComPac "Picnic Cat" is a 14' catboat with a centerboard and very easy to step/unstep mast. ComPac also made a couple of different 16' models, the ComPac 16 with a shallow (18" draft) fixed keel, and the 16XL a similar design that has a retractable CB.