never seen one , infact only colour mutations i have seen are straita and micro , both come from fish farms and are the product of heavy breeding , most of the straita and micro in the trade are farmed for food and sold as by product to the aquarium trade , some micros are still wild caught but just about every straita will have come from a farm , if you know of any farms that breed maruloides then this is where the albinos will turn up , in the wild they would be eaten in no time at all as they stand out
only naturally occoring mutation that i know of is gachua sp super nova which looks to be a piebald varient that has bred and survived in nature.
fish in picture is indeed a straita albino , straita are genrally very cheep as they are farmed , i would expect to pay less then £10 for a normal coloured and no more than £30 for the one pictured , some people may pay more but you would be lucky. it is not really a rare fish.
cheers col