1.Have you tried a bike shop? I was hoping for an address I could try. Around here if ain't current it ain't stocked.
2.Concerns about the ramp on a 28 not matching the existing cog set? I changed the orginal 14,15,16,17,19,21,23,26 to:
14,15,16,17,18,19,22,26 & noticed no difference in the gear change efficiency. I imagine that by changing the 22 & 26 to 23 & 28 the gear change won't suffer. The ramp concerns are focused on racing I think. If I should give racing another go I won't be riding that bike anyway.
3.Mirage 8 not taking a 28? The very first Campag chain tensioning gear I had in 1952 was claimed be suitable for up to 26 teeth. In 1956, on my first Alpine tour, I ran a 28. The only thing was I couldn't be on the 44 ring when using the 28, I had to be on the 36 ring. But that's the idea anyway. The original swinging parallelogram gear didn't really handle enough chain for Alpine gears.
So, I still need a lead to a bike shop.