I kinda understand the OP's frustration...
R6 LLB are at the Enduro B2B website at
R6 LLU/LLB ABEC 5 0.375x0.875x0.2188 - Enduro Bearings B2B. So we know they exist, at least on paper. Unfortunately you have to be a reseller to order direct from Enduro but those are the R6 bearings with LLB seals the OP is looking for.
I can't find these retail anywhere and I think that is the problem the OP is facing. There are tons of R6 LLB bearings out there but they are all ABEC-3. I don't know why they are listed on the Enduro site but not available anywhere.
The ABEC-5 R6 with SRS seals are at
608 SRS ABEC 5 8x22x7 - Enduro Bearings B2B. Same thing, different seals. These are available all over the place. Wheels Mfg sells them.
$8 USD each. Not sure about shipping to the UK though.
Enduro's website says that they do come packed with Rheolube 374A which is Lithium based.
I would go with the SRS seals and be done with it. A local guy who builds 2000 sets of wheels every year showed me how to set preload when I used the Enduro bearings to service my old Mavic Ksyriums.
-Tim-