50 foot cables?

@OP, 
You might get lucky searching Ebay for used cables.
25 feet is long, but I scored a set of AQ Rockefeller cables a while ago.
They were the real deal and AQ cut them down and had them reterminated when I moved to monoblocks.
Also, check Hifi Shark. Use the filters to narrow down your search.
A little patience, and some luck should allow you to find a pair of cables.
(Just keep in mind, there are counterfeits out their, so do your due diligence. -That is try to find sellers who can provide a receipt of purchase from a dealer, if possible).
Bob  

+1 Miller.
However, I would do everything possible to knock down the length of those speaker cables. Even 25 feet long is crazy and IMO probably will have some negative sonic effect.

@ tuberist,

"Even 25 feet long is crazy and IMO probably will have some negative sonic effect."
I have been using 25 foot long speaker cables since 1992.  Let me assure you their is no sound degradation.  I spoke with McIntosh the manufacturer of my amp and was told there will be no sonic degradation of sound.  I checked with my speaker manufacturer(s) and Sandy Gross from GE told me there is no sonic degradation of sound, lastly I have a EE degree and know there is no sonic degradation of sound. 

My speaker cables are 11 gauge and 25 feet is nothing for a 300wpc solid state amp.  I wonder where everyone gets their information from?  For fun, I moved my speakers next to my amp and tried 5 foot cables and trust me, there was no difference between them and the 25 foot pair of the same cable.   If there was, do you think I would have 50K of equipment in my listening room if the cables degraded the sound?

+1 Miller. 
However, I would do everything possible to knock down the length of those speaker cables. Even 25 feet long is crazy and IMO probably will have some negative sonic effect.

Thanks, and if it turns out he only needs 25 feet just coil the rest and pile it in with the rest behind the rack. It can't make any difference. stereo5 said so, and he has 50K of equipment.