Or search: g, r, staunch, ceaseless, constancy, immutable, incessant, invariant, parameter, stability, unceasing, unfailing, invariable, unflagging, unswerving
2 Syllables: SU
almond, common, Compton, conference, conscience, Constance, constant, convent, Johnson, Johnson's, Johnston, Jonson, Longman, omnium, quantum, Taunton, Thompson, Thompson's, Thomson, Thomson's, wanton
3 Syllables: USU
despondent, inconstant, preponderance, remonstrance, respondent, uncommon, Wisconsin
4 Syllables: UUSU
correspondence, correspondent

Found 30 words across 3 groupings. Skipped 5 excess words of a similar stem.