Is it internal/unpublished sequence or from one of the existing genomes? If it is a sequenced genome, this is possible from either BioMart or UCSC Genome Browser style browser. If it is an internal project, the script jockeys can help you I'm sure.
BioMart (or the specific Mart for your species if it's out there):
Go to BioMart.org
Select the database and data set.
In Filters, set the region. Use this item to enter your list: Multiple Chromosomal Regions (Chr:Start:End:Strand)
In Attributes, choose Sequences. You also need to pick a nucleotide box* here, but I'm not sure which for this application.
Set and upstream and downstream flank.
*Although now that I look at Sequences I'm not sure which radio to choose for this purpose. I'm going to have to ask them that. I think I'd choose exon for now.
On Region line, set items in Define Region button.
Choose output format = sequence
click Get Output.
On next page say Genomic
Set upstream/downstream length
Get Sequence button
Or you can do all of either one from Galaxy (http://www.usegalaxy.org), and you can store that as a workflow you can always go back to later if you need it again. There is also a "Get Flanks" in the Galaxy menu "Operate on Genomic Intervals".