I've never herd of one. Why not sheer speculation but being that tremper developed them and most are decedent's from moose who was a Tremper albino so most are at least het for it. I personally believe it is a result of many years of line breeding large leos and not Co dominant so in out crossing you would probably lose size from them. Also morphs go in trends and the Giant thing isn't to popular anymore to go threw all the trouble. But that's my opinion
I just talked with a breeder that said he has a Rainwater albino that is 124 grams so that would be a giant. Now I would assume he has the rainwater part mixed up and it's not a rainwater but a tremper. He wants to sell me some of the off spring of this gecko but I was hesitant because it was rainwater albino but now I find this thread makes me think he is wrong. The daughter is over 90 grams and a year old so she should have some giant there.
Not sure about Rainwater but I just hatched a hypo baby het bell from a giant hypo het bell/ bell hypo and he is 1.5 times bigger then his clutch mate already
There is a definite difference between a true giant and just a big gecko. Giants are genetically predisposed to be large, and generally have a slightly different conformation than non giants. I have had many 100+ gram geckos that were not giants. I know for sure there are giants het for RW out there, because I've produced them. I would guess someone by now has a Giant Rainwater, but I haven't seen any myself.