IIRC, is 4'x6', not 4'x8',
the last time I got it from a signage shop, HDB shop at Upper Weld Road/Jalan Besah, but that is many many many years back, (before internet) not sure the shop still around or not.
anyway, just google and found the shop name.....
Yeo Soon Hin signcraft (Blk 633, Veerasamy Road/62949771)
hope this help.