i dont believe what you want exists....but its easy to make out of the bits.
For a start, you want an inverter that can shovel 120-240VAC into your wires.......they are offtheshelf items...........so you get one of them......look at what DC voltage it requires.........then you simply make a converter which converts mains to that DC voltage...and another converter that converts the solar output voltage to that DC voltage ......
So then you just need some way of switching between the two.
This could be very simple......just switch on the solar one and see if it can provide the power (ie, the output voltage of it doesnt drop out).....if it drops out....then switch to the mains converter and use that for 5 mins......after 5 mins......try the solar one to see if the suns come out yet......etc etc.
Also, i think you should go for MPPT....solar panels are high Z and it'll mess up the power transfer if you dont.
...Of the 2 converters that are feeding the inverter with DC.....(one from panel, one from mains).....you can actually just have them both feeding the inverter input together..and just enable one, and disable the other, and then vice versa......perhaps sense the current of the solar one...and if not enough current is flowing...disable it, then enable the mains one......then after say 5 mins repeat...etc etc.
A micro or Aruino sounds handy for doing the small bit of logic....Arduino is nice and simple to learn...youtube.