Thanks bsa05. I've sent an enquiry to them for a quote.

SteveB - Point taken. The situation is requiring a bit more thought and we'll have to review our future pricing since with (I think) a 30% mark up we're currently selling one at £6.33 and the other (022595) at £1.50 which isn't going to get anyone very rich.
Inevitably there's a lot of capital invested in stock of essential but slow moving parts which are always increasingly expensive each time we are obliged to buy replacements in small quantities and as many will know, some owners can be tight-wads when it comes to spending on 'consumable' stuff to keep their treasured bikes running.