i quite like challenges such as this and i used to be handy with a search engine (before they 'improved' the logic) so though i'd be able to find one easily...
in-terms of a gtv i could only find evidence of one and that is resin based rather than diecast. they do a spider too and it appears you paint it yourself(?)
in-terms of spiders i found another manufacturer on the same site and it looks to be diecast but does not state so.
on the same site (a french 916 club site) there are some other interesting models including a couple of remote control 916 gtvs one of which looks kinda like a racing liveried version of the dtm-ish gtv on the omg ebay thread.
so this is the link for the google translated version of the aforementioned site:
french 916 club site with models
clicking next takes you through the information on different 916 models compiled by this person.
the contact details for the (only?) gtv 1:87 model appear to be as per this link:
no idea if they still exist/make them/etc.
and i'm going to mention this just because i found it strange but the specific google searches i did in image terms of image results strangely all produced an image from this russian woman's google plus page. the image that was returned is the wolf who appears to have an idea(?) which apparently is the grey wolf from 'Ivan Tsarevich & the Grey Wolf'... her page reminds me of the 'i love russia' video compilations from youtube. i'm sure you and all wanted to know this
back on topic if you want to have a diecast collection then you might want to start again
at 1:43 or less common but possibly 1:64. though model collectors seem to like a certain scale for whatever reason so i don't know
edit: oh i forgot, there also appears to be mention of a kyoto spider ph3 in the link to the book below (a history of the 916) but the preview does not allow to show that part of the book. seems interesting for 916 nuts but is £13 for a e-copy!!!