was wondering if this seal is available anywhere or another also fits,i.e CB185.
Should be available from any Honda parts supplier.
Will replacing that seal mean splitting the engine?
No you shouldn't have to strip the engine. As removal of the gear lever shaft seal normally involves removing the right-hand engine (clutch) cover and clutch.
If the CD185 engine design follows normal Honda/Japanese practice, then it should be possible to remove the shaft (after disconnecting any selector parts? & gear lever) from the right-hand side of the engine, as the shaft goes right across gearbox. It should then be possible to lever the seal out of position and fit a new one.
The only problem you might have is if the shaft has been bent by accident damage etc. in which case it may not be possible to pull it out without cutting off the bent (L/H side) part of the shaft first?
I do suggest you get a workshop manual first if you haven't got one?
Try Lings for Honda parts:
http://www.lings.com/http://www.bestpricehondaparts.com/