Even at that, your chances of finding a 186 bell are only marginally better than a M-W bell. Now, from experience, here are the other issues if you don't find an exact match M-W bell:
1) Even with the same manufacturer, the specs as to bell stack height, placement and diameter of the bell ferrule, throat taper, etc., all change over time;
2) All bells have a slightly different taper. Make sure you measure the critical points of diameter at the ferrule, diameter of throat where the last brace between the bell and the bows, and at the leadpipe, so it neither crowds the bell or sticks out at an angle, assuming you want a "vertical" bell relative to the bows;
3) If you go with another bell, then as these measurements change, so does the effective length of the horn, even if the physical overall measurements are nominally the same; and therefore the tuning: too long, and you may have to shorten your main tuning slide; too short, and you will have to lenghten it. My Bessophone ended up with the lucky accident that the diameter at the ferrule was too small and had to be trimmed, shortening the overall length. By lengthening the tuning slide to get it back down to pitch, and therefore adding more cylindrical tubing at a critical point that tends to expand the overtones, this almost cured the notorious "flat fifth partials" characteristic of these horns, including Miraphone, M-W, Weltklang & stencils, etc. Lucky fluke. You can't predict how the change in the overall taper of the horn, or the reproportioning of the cylindrical/conical ratio of the tubing will affect intonation and "blow" (i.e. stuffy notes, dead spots, etc.).
4) Depending on the flare of the throat of the bell, your leadpipe may fit, or have to be repositioned, or, as in my case, a brace soldered between the leadpipe and the bell casing to maintain its proper orientation, especially if the leadpipe was previously soldered directly to the bell along its length.
When I replaced the bell on my Bessophone, we took a very long time to measure, fit, measure, fit, measure, fit, then cut long, then measure, fit, measure, fit, measure, fit, trim to length to match the bell stack ferrule, then measure, fit, measure, fit, measure, fit to make sure it had the correct orientation and the lead pipe and receiver were positioned correctly. In other words, the process of changing a bell, even if it is the exact make, model, range of years of manufacture, etc., can be much more of a chore than "wax on - wax off."
My tech was patient with me, we had a great time with the project, and I made sure his remuneration was commensurate with the superlative job he did for me. Sometime in the past when there was a bandwidth glitch on the forum, the pictures mysteriously went away, and I will have to repost them to my thread about the Bessophone, here:
viewtopic.php?f=27&t=61956" target="_blank