Some may recognise this thread from the Grand Tourers site.. I bought an Excel a few years ago now with an allegedly rebuild engine. Having fitted it and found it had zero oil pressure and then rebuilding the oil pump and PRV both time with zero pressue as the result I then took the sump off to change the nylon olive I discover 15+ stamped on the bearing panel. On looking through the receipts with for the parts fitted during the 'rebuild' i find the mains fitted were not +15 OD. the result is now I have a crank that has to go be re-ground and polished.  I also find that these +15 main bearings are a bit like unicorns to buy, however there seems to be an 'aftersales list' on which they are occasionally sighted, is this at mythical or is there a live link to it? I should add that the original worn bearings came with the car, when compared to the ones I have just taken out they do indeed have a larger OD

The aftersales list is/was a spares list that Lotus were selling at massively reduced prices. They were all available via the dealer network,  as such, if (and I doubt it, but worth a try) they are still available then you can check by simply asking any Lotus parts dealer.

I had the same problem and was told by both Lotusbits and SJSportscars that they are no longer available.

I had to source another block and crank carrier.

Sorry - not what you wanted to hear

There is another solution for this in adapting Chrysler V-8 main bearings which are widely available. Requires line boring the main bearing saddles to suit. See the attached summary written up some years ago by noted enthusiast Tim Engel.

TIM_E_MAIN_BEARING_DATA.pdf

I might have found a set.. but I won't know until I have the crank examined

Check if standard-size bearings are compatible: If the crankshaft wear is minimal, using standard-size bearings with appropriate shims might be an option. Consult a qualified engine machinist to assess feasibility and potential risks. Source a used engine block: If the cost and effort of finding +15 bearings or alternative solutions are prohibitive, consider searching for a used engine block with compatible standard-size bearings. Of course, you can also learn more about bearings at https://en.tradebearings.com/bearing.html. This is still very helpful for how to install bearings correctly and how to buy cost-effective bearings.