forecast monthly shipment (time series) for 300 products individually in R I can build ARIMA model with regressor to forecast monthly shipment for one product. but I have 300 products and each of them needs a monthly forecast.  

my question is, instead of building 300 models, is there another approach in R to deal with the goal I am trying to accomplish? 

thank you!
It is difficult to answer this question with the limited information provided here. Nonetheless, I have following recommendations.

Do you have a (data backed) reason to believe that you do not need 300 different models? For example, are the shipments of different products correlated? Alternatively, can you instead model the problem at higher levels like product categories? If either case, you can take a look at hierarchical time series modeling. This journal article by Rob Hyndman, author of forecast package in R can get you started on hierarchical time series modeling.