When I had the GL500 I was always afraid of snapping an exhaust stud because of a rusted on nut. Between it and Eccles I had a CB750SC for one winter; Its exhaust nuts were had deep acorn nuts. When I initially put Eccles together I wanted to use long acorns on it so I looked up the part number (90304-438-000) and priced new ones from Honda. After I fell off my chair when I saw that they were over $7 CAD each I salvaged as many of the ones from the 750 as I could, cleaned up the best of them and used them.

I knew they had to be available somewhere for a more reasonable price so whenever I thought of it (usually when I took them off or put them back on) I would search online. FWIW, they are currently listed for $4-$6 US (@5.35-$8 CAD)(+ shipping) per nut from most of the online sellers. Then I found this eBay listing.
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They arrived today and they are just about perfect. Other than the fact that my old ones are rusty and these are shiny & new, the only difference I can see is that they are 22mm long compared to the Honda ones 16.2mm.

Note that the studs that come with these nuts are approx. 34.5mm long and the CX family's engines require 55mm studs so they will not fit but the original ones from Honda are cheap (I think they were about $0.95 CAD each from the dealer).