The Rekka cups worked the other way, for 1" forks into a 1 1/8" frame. They were a real bitch to find a few years ago, you'll be very lucky to locate some now -but you never know.
Edwardes told me they once knocked something up for your situation, give them a call to see if they can remember what they did & what parts they used. It's definitely possible.
I think someone on VBMX came up with a certain bearing race that would do it, but I can't find the post. Here's a relevant quote, though:
"follow-up on using Threadless 1 1/8 in a 1" BMX head tube.
I recently installed a 1 1/8 setup in an old GT performer, by using the 1" cups with the 1 1/8 parts. I had to try a couple of different 1" bearing cages to get one that slipped over the 1 1/8 fork and allowed the 1 1/8 race to slide in without rubbing. (cheap cage from a Walmart Mongoose worked best) The outcome was very smooth and tight. top notch conversion without any added expense."
And another lengthy stream-of-consciousness one from another VBMXer:
"I will assure you though you can put a 1 1/8" threadless fork in a old 1" frame with no machining cutting or grinding want to know how? take just an old 1" headset cup and a pair of 1 1/8 forks slide the cup over the fork HEY IT FITS !!!!! now take a frame with 1" headset cups in it and the rest of a threadless setup forks stem the secret is in the headset get the cheapest smallest diacomp aheadset or the tank and mabye a few others (i use the cheap one why pay for tank cups when you don't use them anyway) use everything but the cups so bearings upper and lower race everything but the cups with your 1" frame and 1" cups the biggest 1" cups you can get i think like a tange or mabye a bear trap or odysey i'm not sure i just took old 1" cups untill i found one the 1 1/8" bearings fit in and put it all together. IMPORTANT you cannot use the 1" bearings also on some 1pc machined forks the taper for the race starts to soon and hits the cup (see grinding) i know i said no grinding but you don't have to with most forks and no matter what the bearings fit a little tight in the cups not bad but a little tight it worked great for me but if you don't like it freeball the cups (bearings no cage) this is tough and most won't want to do it if you do leave space for one to two bearings missing top and bottom so no bindind. try it out tell me what you think or if you have any ? let me know if there is alot of intrest i will get more detailes for you i have done this on at least 10 bikes and have 6 years bike shop mechanic experience (i got board one winter playing in the partas drawer) hope this helps someone."
