where to find 273 - 340 double lip silicon rear main seal ?

Same as a 5.2 magnum seal minus the wings. Rock auto enginetech #S0605 5.2 magnum Viton double lip seal , and enginetech S1196 standard 273-340 single lip seal with attached wings .Trim the wings from the single lip seal and use with the double lip seal and a little silicone to seal the joint for about $12.00