It seems it is difficult to find suitable plants. I went to a local nursery
and asked the gardener, all the plants available are perennials. I had
emailed T&M, and at least I got the following suggestion:

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Busy Lizzie's and Petunias make ideal bedding plants that will flower
prolifically all summer long. Petunias would require deadheading to prolong
their flowering period though. You might also like to consider Marigold,
Nemesia, Verbena, Begonias and Cascading Balcon Geraniums, all of which
would look good in pots and baskets, perhaps interplanted with trailing
Lobelia, again all would need deadheading to prolong their flowering time.
Feeding and watering would also have to be taken into consideration to get
the best out of your plants...

All plants will require a degree of care and attention, especially when they
are grown in baskets and containers as these will dry out very quickly
during hot dry weather, even in wet weather they would still require
watering, as the rain would not be able to penetrate through the growth of
plants to significantly water the growing medium. SwellGel would be an
advantage but watering would still be necessary during hot, dry periods.

....

An alternative might be to check with your local nursery or garden supply
outlet, who would supply smaller quantities of plants, but these would still
require some protection from frosts before planting directly into the
garden.
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I am rather impressed that in addition to the list of plants, they had
suggested me to go to my local nursery, even they might not able to get my
MONEY!!!