Here's what rhymes with costaux.
no so know go though low show co blow pro row tho fo foe ho lo bo doe dough mo po ro toe wo woe tow yo beau bio ceux faut goe hoe jo ko sew soe vo beaux cho dau mow noe roe sho topos tuo yeux zo bro rho trow whoa doh although below ago flow grow slow snow throw glow quo audio fro chateau crow hello thro polio uno dicho floe chateaux dunno stow throe chapeau oleo sloe tarot turbot kayo chapeaux fatso pekoe borzoi schmo schmoe radio overthrow plateau studio bestow overflow folio patio stereo forego forgo nouveau propos tableau vertigo aglow domino escrow outgrow rodeo siglo spatio tableaux plateaux trousseau adagio kapok deathblow foreknow overgrow bandeau gateau matzoh gateaux trousseaux romeo resew ratio embryo undergo buffalo indigo portico calico dynamo aliquot apropos cameo medico afterglow piccolo undertow regrow pompano tallyho portfolio bungalow mistletoe presidio oregano pistachio mustachio moustachio politico microdot impresario braggadocio pianissimo archipelago generalissimo