Carpenter offers L6 in flats, almost never less than 3/8-1/2" in thickness however. Crucible offers it only in rounds, but you can get them in almost any diameter. Perhaps one day most folks will come around to the fact that sawblades can be made of virtually anything the manufacturer feels like, resulting in the inability to be certain of what you have regardless of the alloys one wishes it was. This is especially true since the most economical way to make them these days is to insert carbide tips onto any steel that will not come apart in use and doesn't require a fancy heat treat.
Most folks out there make the assumption that L6 and 15n20 are pretty much interchangeable, when in fact the only thing they have in common is nickle, and then not even in the same ammounts. 15n20 is a very nice steel that is pretty much 1075 with nickel added, while L6 is a whole different beast (Cr,Mo...) that has a very contrasting heat treatment.