granddaddy, grape ape, erkle and purple kush are all clone only elites as is mendo purps but because of the good work done that can be gotten in seed form, but if you are no in cali or have some cali hook ups then have fun finding PK, GDP or erkle
What are you looking for in a purple strain, because also remember that all of these strains have major differences in them, while some have stricking similarities... Do you just want to grow something that turns purple or do you have a specific goal in mind...
One thing to look into is Subcool's Qurkle, which is "killer queen x purple erkle", and while I have not grown it, it comes from our buddy subcool and TGA, and i have heard nothing but great stuff about it... Well worth looking into atleast