Plitron has a balanced isolation transformer, Part #8575-X0-02, that is available for sale to DIYers. Equi=Tech has factory B stock and "blems" available for sale direct from the factory from time to time. Toroid Corporation of Maryland also sells balanced isolation transformers. Factory quoted lead time is 2 weeks, but in my experience was more like 3 business days. The transformers in my unit pictured are from Toroid Corp. Schurter, Corcom and Qualtek make EMI/RFI filters that are suitable as pre-filters ahead of an isolation transformer. PM me at sae_2300@optimum.net if you need more specific details.