I can't believe I can't find one online. Anyone have a source?

They come with replacement hubs. When I replaced my front hubs, I found the new ones too difficult to install because they're slightly deformed to be a tight fit, so I re-used the old ones. As has been mentioned, generic replacement caps from an auto parts store would work if you find the right size. Worst case, if you can't get one from the source posted below, I can mail you one for the shipping cost from Canada.
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1992 745, >500k km

You guys are great. Thank you all.

What I SHOULD have posted from the get go is that the grease cup/dust cover was out and lying loose behind the center cap. When I pushed it back on it would "spring out" about half way. I made sure the cotter pin wasn't the culprit and finally guessed it was just a hydraulic response to too much grease. I removed a little grease at a time until it finally stayed in place. It's still very loose and can be rotated by hand. I want to keep an eye on it and have a few extras on hand that FIT. I have never encountered this gremlin before.

As I mentioned, the new covers that came with my new hubs were slightly deformed. Just a tiny bit "triangular". This would make for a tight fit, while also allowing air or grease to escape. Since it seemed like a really fiddly job to align them precisely to hammer them in, I just re-used my old ones. (Incidentally, the original covers have the wheel nut torque stamped on the inside.)
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1992 745, >500k km

Much appreciated.

How about FCP, see this page for 1987 Volvo wheel bearing. Google and places like FCP are your friend.

http://www.fcpeuro.com/Volvo-parts/740/Wheel-Bearings/?year=1987&m=207&e=914&pt[]=307172079

That has been one of my "go to" places for years. I see no dust covers on the page you provided. Thanks.

1) Found PN 271703 for 1983-87 740 "Front Wheel Bearing Kit" in Volvo Quick Reference Parts Catalog* (TP 7777114)

2) Googled 271703 Volvo, got several hits and chose the one for volvooemparts:

3) At volvooemparts I clicked on:
Front wheel bearing kit for Volvo (271703) - Volvo Parts

4) At the resulting screen I clicked on leftmost "Product Images" drawing to get the Front axle spring support page, where I clicked on "Fullsize image"

5) On the Fullsize spring support image drawing I located item 57, then scrolled down to item 57 on the left side of the screen, where item 57 was identified (on the right) as Grease Cup 1359149, for $7.19

6) Then I double-checked the price for 1359149 at TascaParts.com and got:

Part Number 1359149
Part Name GREASE CUP
MSRP $8.58
Core $0.00
Save $2.22
Online Price $6.36

(easy as cake)

* Lotsa google hits on 7777114 (2001 date) for under $10



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Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

If you are looking for the grease cup try a local auto parts store.
Dan