Is a resource like PubChem of any use? You can use the R package rpubchem(https://cran.r-project.org/web/packages/rpubchem/rpubchem.pdf) to download information from this database.
The Protein Parameters tool (http://www.protparam.net) does everything that Expasy ProtParam does but also lets you input DNA sequences for translation and as well as directly enter OD280nm for online calculation of protein concentration. Much faster response time too....