I'm trying to buy some spark plugs for a 67 plate 1100 zetec and confused as it seems impossible to get any, also unsure of the mileage the first set should last? 

Spark plugs on that car would be included with the Ford service at 4 years or 36,000 miles, whichever first.

Though I reckon that's just been copy & pasted from the 1.0 EcoBoost.  On a non-turbo engine with port injection I reckon they'd last a lot longer in the real world.

I'm not sure if they're different to the EcoBoost plugs.  If they are, that may explain why they're more difficult to find.

18 hours ago, KurtUK said:

I'm trying to buy some spark plugs for a 67 plate 1100 zetec and confused as it seems impossible to get any, also unsure of the mileage the first set should last? 

You should be able to get them from a Ford dealer parts dept

9 hours ago, DaveT70 said:

You should be able to get them from a Ford dealer parts dept

Yes, I think that might be the case, although I think europarts stock them, which is handy cos I can't even get my local dealer to answer the phone. I never thought there'd be a time when something as seemingly as generic as a spark plug for a sodding fiesta would be difficult to buy.