Isofix needed for my mk1 hatchback can you buy a bracket for it?

Have a look under the seat, if there are mounting holes/threads there may well be a bracket available.

 

I retrofitted the bracket to my old B5.5 Passat but I reckon the Mk1 Octavia is a generation too old for isofix.

Front or rear?

 

Pretty sure my VRS has isofix points in the rear, though I'm not an expert on these things and have never used them. I'd expect the other models to have them too expect maybe the pre-facelift ones.

my 2004 tdi mk1 had rear isofix hoops fitted.

IIRC, it was optional on some trim levels, while included on others.

 

Select the drop-down for your pre-upgrade trim:

https://www.parkers.co.uk/skoda/octavia/hatchback-1998/specs/

 

You certainly should either be able to buy the appropriate fittings, or just nick them off another trim model.