Thought you might be interested in the following based on some notes I posted some time ago.

The older Volvo 240/140 stock sizes (eg. 185SR14, 165R15) are for a European metric tire. As you noted, a few European tire sizes are still available in some models from some manufacturers (Michelin X-Metrics are one), but you can easily find equivalent common P-metric (American passenger) sizes that will do. The European standard profile (aspect ratio) for all radials is supposedly 82%, so the closest equivalent common P-metric profile would be a /80, but /70 /75 and /85 are often used as stock equivalents in the charts. Unless the width is changed accordingly there will be a small speedometer error (typically less than 5%).

For 14" and 15" rims, high profile /80 tires are none too common, so dropping down to at least a /70 profile should be considered (increase the width by 10-20mm to keep the original diameter). Many tire selectors will list these as "+0" (plus zero) sizes -wider and lower profile tires roughly equivalent to the stock diameter, but which should still fit your vehicle. Although you may not notice much difference with a +0 tire, handling should improve a bit, but the ride won't be quite as soft. Extra wide, low profile +1 size tires matching the stock diameter may also be listed, but you have to start worrying about sidewall clearances for these.

Some tire manufacturers simply don't have a suitably sized tire for all Volvo models and either don't show an equivalent or show an equivalent that really isn't. Use one of the on-line tire calculators to determine the %diff from stock circumference for common sizes. Getting a proper match also requires that your current rim diameter and width are the same as the stock rim. If you stray significantly from stock tire (or rim) sizes you need to check your rim width against the acceptable range of rim widths shown for each tire to ensure that the bead will properly seat and stay sealed.

Also, most speedos tend to be conservatively calibrated. You can often increase the tire circumference by 3-5% without exceeding legit speedo readings. When I get new tires I try to find one of those community radar patrols with the reader board to check my speedo error. For the price of a ticket, you can probably get a more accurate reading on your local interstate.