What are the custom roms available in market for android and ios for micromax funbook P 300?
Firstly you can't install iOS on your Funbook. Any ROM(s) that claim in doing so are actually just running Android with a launcher that looks like iOS.

For information about ROMs for the P300 I suggest you read this thread. The number of working ROMs as is seems pretty scarce.

Also, when you root, unlock your bootloader or flash a custom ROM you void any warranty of your device.