I would try contacting them at there main customer service number which should be on the website.
If that doesn't work, try finding a distribution center (not dealer, but the people who supply the dealers).
I recently purchased a used Brown 472 rotary cutter and called the nearest distribution center. He took my name and address and mailed me all decals at no charge. I just got them in the mail yesterday.
I believe most manufacturers will mail you the decals for free since most labels are safety related.
Don't give up calling though. If the above suggestions don't pan out, keep calling other dealerships until someone helps.
A new paint job and decals will have an old implement looking like new!