If, by 'round' and 'old fashioned', you're referring to a design akin to the shape that most of us here remember as what a kettle looked like when it sat on a stove (possibly with a whistle in the spout), I've also found difficulty in finding a kettle tipper that will definitely do the job for you.
Further, anything that looks like it
might do the job (but with no guarantee that it actually will) seems to be vastly more expensive the models that are clearly only designed to work with jug kettles.
So (daft as it might sound) it might make more sense to buy a new (jug) cordless kettle and to get a 'standard' kettle tipper (of a type specifically designed for use with cordless jug kettles).
i.e.given that some kettle tippers that look as if they might work with your existing kettle (but with no guarantee that they actually will) seem to be priced at nearly £40, it would be cheaper to fork out a fiver or so for a 'value' cordless jug kettle from Asda and to use it with a well-reviewed kettle tipper, such as this one, for around £22:
Amazon.co.uk User Recommendation