You’re unlikely to find anything online as this comes down to how your organisation is structured and its internal employee policies. Do you have an intranet or employee advice line? Many large companies will have all of their policies on the intranet, plus some form of employee services telephone line (eg for queries about payroll, how to raise a grievance etc).
Your entitlement will come down to whether you are considered as being employed by the same employer if you move stores. Most of the time in national supermarkets, you are employed by the national company so a store transfer shouldn’t interrupt your length of service with them and therefore your entitlements. But, the only way to know for sure is to check your company policies.
The key is to how they determine length of service, and change of employer within an organisation doesn’t normally automatically reset your length of service. For example, within the public sector it is common for people to be employed by a sub-section or a larger body rather than the national body (eg the NHS is divided into trusts, and you’re usually officially employed by the trust, or another part of the NHS like NHS Digital, rather than by the ‘NHS’ as a whole; this is similarly the case with some local authorities, government bodies etc). However, many will recognise length of service across the group - eg perhaps you work for one part of a larger public sector organisation, you then move to another part of the same larger organisation, you’re technically moving to a new employer (new employee number, new employer reference etc) but all work you have done for the wider group counts as length of service for entitlement to certain employee benefits.
I can’t think of a reason why you would have to tell a new store that you are pregnant. The only requirement of you to tell any employer of your pregnancy is to inform them at least 15 weeks before your EDD including notifying them of your intention to take maternity leave. Most people tell employers sooner than that, partly because it may be becoming obvious anyway that they are pregnant, but also because once your employer knows then they have a duty to ensure you are treated appropriately (eg risk assessment, pregnancy sick absence is usually exempted from normal absence policies, etc).
The only other thing to take into account is whether your role/work could be different in a local store. Eg your local store may have room for a 3 day a week person rather than 4 days, is there a possibility you could end up losing hours/pay in a transfer or are you able to request one stipulating that you would only transfer to a role of equivalent pay/hours or more? This point is important because your maternity pay for statutory purposes is calculated based on your earnings between weeks 17 and 25 of pregnancy, so if your pay dipped in that time then it’s possible your maternity pay could be lower (but it all depends on what the maternity pay offer is from your company and how much you currently earn).
Hope that all makes sense, this is all off the top of my head but relatively confident it’s correct! Bottom line is you need to check your company policies. If it’s considered the same employer you shouldn’t lose entitlements. What you earn during weeks 17 and 25 will determine your maternity pay award, depending on whether you get statutory pay or enhanced pay and what your company policy is in the case of the latter.