m = DeleteDuplicates[Map[Sort, Tuples[{a, b, c, d}, 3]]];
DeleteCases[m, {Alternatives@@Map[OrderlessPatternSequence[_Alternatives@@Function[x, #OrderlessPatternSequence[_, #]x, &x],
Listable], {b, c, d}]}]
(*{{a, a, a}, {a, a, b}, {a, a, c}, {a, a, d}, {a, b, c}, {a, b, d}, {a,c,d},{b, c, d}}*)
(* adopting Wizard's approach *)
DeleteCases[m, {OrderlessPatternSequence[x : b | c | d, x_, _] }]
(*{{a, a, a}, {a, a, b}, {a, a, c}, {a, a, d}, {a, b, c}, {a, b, d}, {a,c,d}, {b, c, d}}*)