Will it be easy to apply 5 days VOA to Shenzhen at Luohu Port?

I am holding Singapore passport but my husband and two children are holding Australian passport. We will be staying at Hong Kong for 3 days and planning to visit one of our Company's supplier at Shenzhen for a day trip. We could apply for it at Singapore but my not have enough time (probably about 5 days to apply for it at singapore before departing for Hong Kong). Could anyone able to advise me which is the best way to apply for one to Shenzen?

Regards
Winnie