The 1000 genomes project did not create any assemblies from the genome sequence data it generated.
The Gerstein Lab at Yale University created a diploid version of the NA12878 sequence, which is available from the Gerstein website under NA12878_diploid. When used, groups should cite AlleleSeq: analysis of allele-specific expression and binding in a network framework, Rozowsky et al., Molecular Systems Biology 7:522.