There are various github repository of the model trained with the triplet loss. You can simply use their trained model if that would work for your case. Otherwise you may want to train the model by yourself using the triplet loss using the dataset of your interest.

This paper provides you view about datasets with clear experimental discusion

http://openaccess.thecvf.com/content_ICCV_2017_workshops/papers/w6/Liao_Triplet-Based_Deep_Similarity_ICCV_2017_paper.pdf

Here is a github repository quite close to your request. Have a look.

https://github.com/nikolaypavlov/transfer-learning/blob/master/inception-mnist-triplet-loss.ipynb