Those o-rings are here to keep the shock eyelets from twisting in the mount not to keep dirt out or lube in. The bearing has a Teflon liner, that's what provides the "lubrication". If you really want to replace the o-rings look at McMaster Carr
AS568-315 is for FOX shocks (20mm ID, 5mm thickness).
AS568-312 is for the stock Walker Evans shocks (15mm ID, 5mm thickness)
While we're here, the mounting spacers are different too. Both are 12mm hole (for 12mm bolt), with 1.25" tab spacing. Both are also 14.5mm tall.
These are also sometime referred to as 'reducers' or 'misalignments' (though I don't think they are true misalignments, ??)
Image hot linked from Kartek
25mm diameter (widest of the three rings)
20mm diameter (middle ring)
16mm diameter (smallest ring - goes in to the center of the shock)
Stock Walker Evans:
21.5mm diameter (widest of the three rings)
15mm diameter (middle ring)
15mm diameter (smallest ring)
Mixing units is one of my pet peeves. Do it all metric (preferably), or all standard!
ShakyDog , I would take 16 of the Walker O-rings. If your willing I'd send you a money order , cashiers ck , personal check ,what ever , add on the postage , put them in a small manila envelope and drop them in the mail . I'm in northwest Iowa , not too far from you . Let me know and can swap addresses .