First, whether English is a second language should be wholly irrelevant. Are you suggesting there is a necessary difference between 'real' English and English as a second language? Isn't the only difference how the language is learned?
'The pancake lady is here' was and remains correct. I first heard and used that form in 1973, although she happened to be a tea lady.
'The man with the chimney cakes is here' is a lot less likely but still correct. Very much more likely would be 'The chimney-cake man is here' or 'The chimney cakes are here.' What difference d'you think there should be between 'pancake' or 'tea' ladies and 'chimney-cake' or any other kind of men?
'The pancake lady has arrived' is grammatically fine and idiomatically extremely unlikely in standard English. If you want to argue for a difference in English as a second language then please specify at least why you think there are only the two forms of English, or where your particular version is spoken…
'Pancakes are up for sale' isn't ungrammatical but it's wholly unidiomatic. In standard, colloquial English the correct wording would be 'Pancakes!'
'Chimney cakes are up for sale at the reception' or anything like that wouldn't be ungrammatical but again, it would sound rather strange to any fluent English speaker, native or otherwise.
If this is a normal occurrence, expected by at least many and prolly most of the audience, the normal phrase would be simply 'Chimney cakes!'
If it's not a normal occurrence; if it's something unusual, the normal phrase would be something like 'Hey! There's a guy selling chimney cakes in reception! (Never, ever, 'the' reception.)
It is correct to say 'here' in your examples.
There might be a better way to describe 'it when something happens temporarily for an interest but on a frequent basis' but only if 'it when something happens temporarily for an interest but on a frequent basis' made sense, which sadly it does not.
Can you rephrase 'it when something happens temporarily for an interest but on a frequent basis' in at least two different forms, please?