Glen Reseach offers several dendrimers and branching phosphoramidites.
5'-Dimethoxytrityl-N4-(O-levulinyl-6-oxyhexyl)-5-Methyl-2'-deoxyCytidine,3'-[(2-cyanoethyl)-(N,N-diisopropyl)]-phosphoramidite
1-[5-(4,4’-dimethoxytrityloxy)pentylamido]-3-[5-levulinyloxypentylamido]-propyl-2-[(2-cyanoethyl)-(N,N-diisopropyl)]-phosphoramidite