Get the index of the 110 p-values you're interested in
idx <- which(knockdown$pval < 1e-5)
A rotation is as follows (I think I've got those 1's correct -- R is 1-based); access the values at your new index, e.g.,
step <- 10000
for (i in seq_len(1000)) {
idx <- ((idx + step - 1) %% nrow(knockdown)) + 1
## do something with these?
knockdown$gene_symbol[idx]
}