There is a worldwide shortage on 6105, 6205 and 6305, we are still catching up from a hug Christmas rush we did not anticipate. Present lead time is about 4-6 weeks. It is best to place an order if you know you want them. It is not likely they will be a regular stock item again for at least 2 months. It is a production issue and based on a huge surge in demand between November and January that we were unable to meet and have to get caught up on. Basically, we had not seen a real Christmas rush in 3 years and were caught off guard, stock of materials and staff had been cut back over that time.
For a back up, our solution is essentially a DIY set- 6105.500. This is just an autoswitching unit with a fuse to protect the pump. You can connect any battery from a lantern battery, to a gel cell and also solar panels. You have to connect and provide the batteries and charger for the batteries. It may not be as elegant as other solutions, but it is far more versatile since you can change the battery and even make a solar back up option.