Hi Stacy,
I just did a google search for should rests and came up this vendor, Softalk, that makes shoulder rests. http://www.softalk.us/products/softalk2.htm
I am not sure which one would fit the SPA504 phones. I guess you would need to take the dimensions of the phones hand set and compare it to the sizes Softalk has available
Hope this helps.
Regards,
Cindy Toy
Small Business Support
Community Manager
Regards,
Cindy
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