Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
spĕcŭlābundus, a, um, adj. [speculor], on the look-out, on the watch; watching for any thing (post-Aug.): Festus Hadrumeto, ubi speculabundus substiterat, etc., Tac. H. 4, 50: ab ostio speculabunda, Mart. Cap. 2, § 112.
With acc.: speculabundus ex altissimā rupe identidem signa, Suet. Tib. 65.