You can make your own quite easily although maplin kit price is pretty good imho.
To make your own you can have intermittant or variable intermittant
You need a relay from a car with delayed wipers and if using variable the pot (dash timing wheel). Connect the realy in the normal fashion connecting switched live to the wiper live, connect switched live to your master intermitant on off switch, then the 5th wire goes to the pot and then to earth. If you switch the wipers on then it will just go into normal mode.
I've never actually got around to doing it in the 90 as there are always too many other jobs to do!
Matthew