AniDB.net has a list of 40 or so groups that created versions of "Pocket Monsters" (a better title to search for, when looking for subbed than "Pokemon"), 20 or so of which were involved with English subs or dubs  over the years.  They list several with Dual Audio, several with English audio no subs, and some with English subbed, no English audio.  Given what the other fellow said, this may be a mistake somehow in the AniDB listing.  Unfortunately, many of these groups are dead and gone (like Anime-Anarchy, for example), and I haven't yet been able to locate any of the old versions reported by AniDB to have been subbed.

Your best hope therefore, other than PM-Sub's retro project, is to check any mkv version you find.  As you probably know, if it really is Dual-Audio it has to have Japanese and English audio tracks and English subs.  However, the dub track may be set to play by default.  You can look for subs and a Japanese audio track during playback and switch to them if they are there.  You can also set a playback preference in the Haali splitter configuration (CCCP or stand-alone) and in some video player option menus.

I ran across a few other notes by people wanting a subbed version of the early episodes.  Some of them were years old and no signs of success.