If you have certificates, and don't mind doing business over the phone, lots of people will sell them for you. For a start, your bank will probably offer this service. Also, the registrars for the company (there are basically two: Computershare and Equiniti) will normally offer the service for the shares they handle. There are also many independents.
The real issue might be finding someone with a low commission for a small volume sale (which is unlikely to result in repeat business).
If you have them in non-certificated form, the organisation that maintains them within CREST, is likely to be the best choice. Otherwise you will have to do a transfer before the sale.
Be aware that there are potential capital gains issues, although the way you describe it, they will probably not apply. (Inherited shares had they acquisition cost reset on death (the taxman potentially got inheritance tax, instead). Windfall shares had a zero acquisition cost, and so there is a higher risk of a significant capital gain.)
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