The connectors are known as either JPT or "Junior Power Timer" connectors.
The world has largely passed them by but they are still available from places such as RS Components. I did a quick search on eBay and there is at least one seller with 3-way JPT connectors at almost reasonable prices.
I spent a long, long time hunting these connectors down, were I in your shoes I would not bother. the only things that JPT brings to the table is that the connector is moderately waterproof and has a locking bail to prevent the thing from coming apart from vibration.
I would go to your nearest auto electrician and but two each of three way waterproof automotive connectors and switch over to them.
Actually, me being me I wouldn't do that, I would simply strip the existing plug and socket out and solder the wires together on the theory that in the once every 10 years or so that I am likely to need to break the connection I will still have a sharp pair of side cutters and a working soldering iron. "Boss" Kettering (yes the bugger who more or less inventing the Kettering ignition) once said "Parts left out cost nothing and create no maintenance issues".
If you really want to maintain a "plug and play" environment and do not want to pay the cost of waterproof automotive connectors - molex plug and socket such as used to power hard-drives, CD-Roms etc in computers would be more than adequate, buy two sets. You could even use good old house electrician termination strip.
Why buy two sets I hear you ask? Because with a 9volt battery and an LED you can make a device for setting initial timing via the "quick and dirty" approach, also you will then own a beancan tester that can tell you if the evil day to replace a 2AV54 hall effect transistor has arrived or not.
