In the first chapter of the novel 悪人 the author talks about how the stores are being arranged and how it starts to have a parking lot
何店舗かあるコンビニだけを注意して見ていくと、荒江交差点を出てしばらくは通りに面して直接店舗の入口があるのだが、それが野芥の交差点を過ぎた辺りから、店先に一、二台分の駐車場がつくようになり...
So what does 何店舗かある mean is he talking about the number of コンビニ？
店舗 is a counter here and 何店舗か is an instance of the pattern 何 + counter + か = several (cf. this page).
So 何店舗かあるコンビニ literally means "convenience stores that are/exist several in number (along the road)". In the particular sentence, basically it means "if you pay attention just to convenience stores (disregarding other things, house, other shops etc.) as you drive". And it says near 荒江交差点 the space is tight, and from 野芥 on, stores start having one or more parking space.
