Something like
filenames <- paste0("file_",1:N,".csv")
## or maybe list.files(pattern="^file_.*.csv"))
rulesList <- lapply(filenames,
function(x) apriori(read.transactions(x,...),...))
which will return a list of rules you can access. Or:
transList <- lapply(filenames,read.transactions,...)
rulesList <- lapply(transList,apriori,...)