They run better with the stock airbox, right amount restriction and all that. I have seen a few where guys made some tubes out of rubber hose, i guess anything is possible, but otherwise watching eBay and trying to find some ones in better shape or an entire airbox is the best bet. I had to find one for one of my 200's, took a while watching eBay but finally snagged one. There doesn't appear to be any aftermarket options.
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1984 Honda ATC200ES "Big Red"
1982 ATC200E "Hondie"
1988 TRX300FW "Project Quad" Still in progress....