I did a search for you on BenchSci and found several antibodies for somatostatin that have been published using IF. (EMD Millipore, SKU AB5494; BioTrend, SKU SS-800-50 are top cited)
You might be interested in reviewing the data before making a decision:
Immunostar (http://www.immunostar.com/shop/antibody-catalog/somatostatin-antibody/) and R&D Systems (https://www.rndsystems.com/products/human-mouse-somatostatin-antibody-906552_mab2358?utm) are a couple of other sources you might explore. The ImmunoStar pAb has a long history and has been cited many times.