Don't forget about Sigma - they've a 150mm and 180mm macro lenses on the market; though you might have trouble getting a new 180mm, the 150mm might still have some stock left over. If neither are on the new market there is always the second hand. They are both top of the range options, and the sigma 180mm was always the more popular choice over the Tamron (I forget why but there is something about the Tamron that lacks which makes it less popular as a choice, even though its optics are, like all macro lenses, very good).
Both of the sigma options have been replaced with, more expensive OS versions (hence why stocks are low in the new market) although optics haven't changed all that much (like many macro lenses there just isn't all that much that can be improved upon - though of course there is a gain its not generally that large).