I've seen acrylic "glass" block at masonry supply places here in Boston, check your local phone book.
Acrylic is MUCH lighter than glass. You can drill it and put in lighting, kinda funky.
I've also been sticker-shocked by replacement glass block units intended for replacing basement windows....basically, some guy assembles glass-block units with the plastic spacers and silicone RTV.
OUTRAGEOUS prices, so I made my own. Used a nice flat piece of ply to assemble the units, waited for everything to cure THOROUGHLY before moving/installing!
Assemble yours outside the bus if need be, then bring in as a unit and install. You can use GALVANISED angle brackets, installed while building the block unit. You need galvy, as the acetic acid from the RTV would otherwise start corroding plain steel brackets immediately.