accordion bellows direction

FWIW, I'm no expert, but a brief web search shows me that different publishers use different systems, with at lest half a dozen in common use. The particular symbols you are showing appear to actually have been intended to be the standard violin upbow and downbow symbols - these are used by several published and recommended in several styles guides I found. But apparently those weren't available in the font used the publisher of your second excerpt, so they substitute some plain geometric shapes. The violin downbow symbol is exactly what your first except show, though.

So, I think your best course of action is to just use the standard bowing symbols, which you can either add directly as articulations (which is how several publishers I saw do it(, or embededded within text (via the F2 "Special Characters" dialog) as your excerpts seem to be doing.

BTW, if you should wish to reproduce the look of the publishers who use the geometric approximations instead of the actual bowing symbols, you could insert as graphics (which I think you've done?). But perhaps better, as text using standard Unicode box drawing characters. The FreeSerif font included with MuseScore has a pretty set of those. But from what I'm seeing the violin bowing symbols are probably the way to go.

If you can find links to published examples and style guides explaining their use that support the idea of the geometric version being legitimate separate symbols in their own right as opposed to just approximations of the bowing symbols, you could propose their inclusion in the SMuFL standard for music fonts, so that future versions of MuseScore and other standards-compliant notation software would be able to use them directly.

Those symbole do exists, in the Artiulations palette, upbow/downbow, for (bowed) string instruments basically. So just use those for accordion too