When you say Gamera 4, do you mean Gamera: The Little Braves
Here is the Japanese Region 2 DVD with no English subs for $51.99: http://global.yesasia.com/en/PrdDept.aspx/code-j/section-videos/pid-1004475532/
OR you can go with the Hong Kong Region 3 DVD with English subs for only $9.99: http://global.yesasia.com/en/PrdDept.aspx/code-c/section-videos/pid-1004593666/
There is a fan made film called Gamera 4
: The Truth which features a beefed up Gamera from 1999 against Albino Gyaos. This film was praised and officially released on DVD by Daei. Running time was a little over an hour I believe. I have yet to find a copy of it but would love to see it.
It features both CGI and professional quality suits. I'll see if I have some pics to share.