We are very sensitive to having second sources. I did an exhaustive analysis of the accelerometer chip market when specifying a part for a design about a year ago. Saving you all the agony of the long story: I narrowed it down to the STMicro LIS2DH (2mm package) and the STMicro LIS3DH (3mm package). The former is stocked deeper, which suggests higher volumes and thus perhaps better longevity, but the latter is pin compatible with at least ST's own LIS331, Analog's ADXL344 and ADXL346, and several parts from Kionix. In other words, the LIS3DH appears to conform to a psuedo-standard for three axis accelerometers in the industry.
Keep in mind that pin compatibility may not equal firmware compatibility, but they all have a WHO_AM_I command that your firmware can use to query which part is installed today and alter its behavior accordingly.
I went with the LIS3DH and haven't had any availability issues. About a buck in 100's. FWIW, DigiKey presently has 132K pieces in stock so it doesn't appear to be going anywhere soon. ST's spec sheets and appnotes can be a bit cryptic at times, but the part does work well.
Hope this helps!