There are a great variety of jib traveller systems available. Any Hobie dealer can fix you up (some advertise on this site). The Hobie and Murrays catalogs (on line) have pictures of different systems.
Once you remove and throw away the original Seaway traveller car/cleat, you will need (each side) a traveller car, jib sheet cleat (mounted to the traveller car or on a separate swivel base), traveller control line, cheek block, traveller control line cleat and return bungee cord. Probably about $200-250.