Currently the WANTJOB variable is only available in ASEC samples in IPUMS CPS. As you point out, however, this variable does exist in the raw CPS monthly samples. So, it is possible to merge your IPUMS-CPS data extract with its corresponding NBER dataset. The easiest method is to attempt a sequential merge (i.e. first NBER observation to first IPUMS-CPS observation, second to second, etc.). Since our datasets share the same sort order as the original NBER datasets, this should be successful. You should verify such a merge by confirming that sex, age, and race match between datasets.
Hope this helps.