Air Filters
As far as air filters, I recommend that you upgrade to a K&N Filtercharger (part number: 33-2784). This filter is readily available in Europe but difficult to find in the USA. Again, JAE carries these and usually has them in stock.
As far as air filters for 4-cylinder Esprits are concerned, here's some parts to cross-reference to:
Lotus...............A907E61827H
Lucas...............F9164
Beck................042-0976
Big A...............94005
Coopers.............AG487
Fram................CA3166
Wix.................46005 (discontinued)
AC Delco...........A1337C
Hastings............AF44
Purolator...........AF3223
Geon................48-0358-9
Mann................C-4368
World Parts.........W27-606
Jaguar..............XKE 70-71 & XJ-6 70-78
Triumph.............TR-7 77-78 & Stag 70-73
Note: The Lotus air filter has a thick rubber gasket along its perimeter. This gasket is usually sold as a separate part from the filter by most Lotus parts vendors, but is not included with the filters listed above. You can simply remove it from the old filter and re-use it.
For V8 models there are several options beyond OEM. These are made by ITG, Amsoil, or K&N.