Pinnacle Headset Nightmare

Hi. I have a Pinnacle Laterite 3 from Evans which is 18 months old and which I’ve been using as my winter workhorse. It’s been fine until now, but just before Christmas I noticed a grinding noise from the headset. On taking it apart I was greeted with a rusty ball cage (bottom of headset), which was missing several balls.

I thought it would be easy enough to get replacement parts. According to Evans website the headset is FSA No.10, internal 1-1/8. After some searching I found some tech data sheets for this headset which showed the ball retainer should be ref. MR013, 5/32″ X 20. This seemed to be a common size so I promptly ordered a replacement cage, which arrived today. When I went to fit it however I found it was too big. The outside diameter of the new bearing cage was about 39mm, while the old one was 37.5mm or so.  On closer inspection the old cage bearings appear to be 1/8″ x 24, a combination that seems to be unique!

Next I popped into local Evans store and explained the problem. After some searching the mechanic said they didn’t keep these parts and my best option would be to have them fit a complete new headset, and suggested a few mid price options. 

What should I do? I see quite a few people recommend just using loose balls and packing with grease, but I’m not sure if this is a good idea. I cannot understand why headsets are not just standard sizes and why I can’t just buy a replacement cage. It’s not like I’m trying to restore something from the past either, the bike is almost new!