Sorry if these are very newb posts, but I dont see a faq.
Are there any quality, one piece strut bars that fit a first gen IS300?

 

One piece front? That I don't know...
I do know there are a bunch of 3pc bars that fit. The most famous is the CUSCO bar that works on the JCE10
(that means it clears the 2JZGE intake manifold in US cars)

Most Japanese Altezza bars don't fit, due to the majority of Altezzas having the 3S-GE or the low profile 6 cylinder 1G-FE

But for the rear, yes there are a few out there

 

Carbing Type 1 will fit with the covers on and Type 2 will fit with a little mod on the covers. Both are one piece.