So far as I can discover there has been no more recent printing of either work below. The circumstances behind Foulds' brief connection with Éditions Maurice Senart, the French publisher, are worth study, although the possible reasoning behind his choice of the cello sonata (newly revised either for publication or published due to revision) are covered by Macdonald (1998). Since publication, the rights have been passed on with the tide of publisher conglomeration: Senart were taken over by Salabert, which then came under the umbrella of BMG. Miranda Jackson of BMG Editions has Salabert, as well as Ricordi and Durand, in her remit and confirms (with colleague Nick Cuttsboth e-mail addresses are logically formed and probably available on the BMG.com website) that the company is no longer in a position to sell copies, so is at liberty only to authorise personal copying of existing items or negotiate terms for other uses.
Essais sur des modes (Essays in the Modes) (1928) [piano]
Sonata pour Violoncelle et Piano (Cello sonata, op.6) (1928)